Viscoelastic silicon rubber compositions

ABSTRACT

The invention provides for new viscoelastic silicone rubbers and compositions and methods for making and using them. The invention provides for viscoelastic silicone rubbers that are stiffer on short timescales than they are on long timescales. When subjected to brief stresses, they are relatively stiff and elastic, and they resist changing shapes. When subjected to sustain stresses, however, they are relatively soft and accommodating, and they gradually change shapes. When those stresses are removed, they gradually return to their original shapes. These viscoelastic silicone rubbers resist compression set and they are extremely resilient in response to sudden impacts. They can be dense rubbers, foam rubbers, and particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application No. 61/521,799,filed Aug. 10, 2011, and 61/532,167, filed Sep. 8, 2011, which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Soon after Rochow invented polyorganosiloxanes or “silicones” (U.S. Pat.Nos. 2,258,218-2,258,222), McGregor discovered that heating boric acidtogether with silicones produced a viscoelastic fluid that became knownas “bouncing putty” (U.S. Pat. No. 2,431,878). This remarkable fluidrebounds almost perfectly when dropped on a hard surface yet, like anyfluid, it has no fixed shape. More specifically, bouncing putty respondselastically to sudden impacts, but flows slowly in response to prolongedstresses. Bouncing putty has a viscosity that increases with rate ofshear, so it is a shear-thickening fluid or, equivalently, a dilatantfluid.

Since its discovery, bouncing putty has been improved and modified in anumber of ways. Wright (U.S. Pat. No. 2,541,851) added a filler such aszinc hydroxide to the putty to improve its bounce. Martin (U.S. Pat. No.2,644,805) showed that bouncing putty can be formed from boric acid andtetramethyl disiloxane diol-1,3. Boot (U.S. Pat. No. 3,177,176) foundthat adding silica reinforcing filler to the silicones before adding theboron compounds caused the bouncing putty to form more quickly and at alower temperature during the subsequent heating step. Boot (U.S. Pat.No. 3,213,048) discovered that bouncing putty can be formed at roomtemperature by adding alkyl borates to silanol-terminatedpolydimethylsiloxanes (PDMS).

Beers (U.S. Pat. No. 3,350,344) found that adding an ammonium carbonatesalt to bouncing putty prevents the putty from flowing under the stressof its own weight and from staining fabrics. Dean (U.S. Pat. No.3,661,790) prepared glowing bouncing putty by adding activated zincsulfide and also reduced the putty's density by incorporating smalltransparent spheres. Kaiser (U.S. Pat. No. 3,677,997) added polyglycolsto bouncing putty and thereby reduced its tendency to become tacky uponextended kneading or use. Mastrangelo (U.S. Pat. No. 4,054,714)discloses that adding noble metal particles to bouncing putty rendersthat putty electrically conducting. Minuto (U.S. Pat. No. 4,371,493)discloses a method for producing bouncing putty from a dimethyl siliconegum, a boron compound, and a reinforcing filler. Christy (U.S. Pat. No.5,319,021) added discrete elastic particles to bouncing putty to obtaina material that largely recovers its initial form when a deformingstress is removed. Christy (U.S. Pat. No. 5,607,993) subsequently addedthermoplastic microspheres to bouncing putty to reduce its averagedensity to approximately 0.6 g/cc.

Bouncing putty is not, however, the only example of boron being added tosilicones. Rochow (U.S. Pat. No. 2,371,068) employed boric acid estersas dehydrating agents for silicols. Nicodemus (U.S. Pat. No. 2,442,613)added boric acid or an organic borate to a heat-hardenable silicone toprevent copper from corroding when the silicone is vulcanized onto thatcopper. McGregor (U.S. Pat. No. 2,459,387) employed boron trifluoride asa dehydrating agent. Upson (U.S. Pat. No. 2,517,945) combined asilanediol with a boronic acid to obtain a thermoplastic copolymer, butnoted no unusual viscoelastic properties in the finished copolymer.Dickmann (U.S. Pat. No. 2,721,857) found that adding 0.005 to 0.090 wt %boron compound to unvulcanized silicone elastomer stock improved thehandling of that stock and reduced its stickiness, but teaches that“when the boron compound is present in an amount exceeding the upperlimit set forth above [0.090 wt %], the physical properties of theresulting silicone elastomer are seriously impaired.”

Nitzsche (U.S. Pat. No. 2,842,521) found that boric acid hydroxylcomplexes act as catalysts for the curing of organosiloxane resins, butnoted no unusual viscoelastic properties in the finished polymer. Brown(U.S. Pat. No. 2,983,697) added 0.01 to 0.16 wt % boron astris-triorganosilyl-borates to silicone elastomers to retard crepehardening, but teaches that “When the amount of boron is greater than0.16 part per 100 parts of siloxane . . . , the additional boron . . .degrades other physical properties.”

Nitzsche (U.S. Pat. No. 3,050,490) disclosed that adding boron nitrideto hydroxyl enblocked polymeric dimethylsiloxane gum, forming themixture into a tape, and pre-vulcanizing that mixture resulted in aself-adhering tape that could be wound on an object and vulcanized intoa homogeneous, unitary tube. Nitzsche (U.S. Pat. No. 3,050,491)disclosed that adding 0.001 to 0.1 wt % boric acid or alkyl boratesproduced self-adhering material, but teaches that “Larger quantities ofboron compound impede the vulcanization and depress the physicalproperties of the ultimate rubber.” Nitzsche (U.S. Pat. No. 3,070,559)discloses crosslinking agents that can be used to make silicone rubbersand includes without comment in a long list of compounds “esters ofboric acid.” Nitzsche (U.S. Pat. No. 3,070,567) then discloses thatincorporating 0.1 to 10 wt % of a complex compound of boric acid and apolyhydric alcohol in a silicone base can yield self-adhering tapes thatstick to themselves only at elevated temperature.

In a patent on self-adhering silicone rubber, Nitzsche (U.S. Pat. No.3,230,121) discloses the use of boron-containing self-adhering siliconerubber insulating tape to protect hollow glass articles. He notes that“The silicone rubbers of the present discovery possess the surprisingproperty that the more violent the blow, the greater will be the reboundelasticity. They possess this property in common with theabove-mentioned ‘bouncing putty,’ to which they are chemically related.”Nitzsche's comment is made in the context of protecting glassware fromimpact and is not generalized to any other purpose. Moreover, thesilicone rubbers Nitzsche employed in U.S. Pat. No. 3,230,121 arethemselves prior art and Nitzsche provides a comprehensive list of priorart patents. The most recent of those prior art patents is Nitzsche'sown work: U.S. Pat. No. 3,050,491 (listed in U.S. Pat. No. 3,230,121 as“Serial No. 9,428, filed Feb. 18, 1960”). In U.S. Pat. No. 3,050,491,Nitzsche teaches against using more than 0.1 wt % boron compounds insilicone elastomers.

Eisinger (U.S. Pat. No. 3,231,542) discloses boron-containingself-adhering silicone rubbers with improved surface characteristics.Fekete (U.S. Pat. No. 3,296,182) incorporates approximately 0.35 wt %boric acid to silicones, along with a titanium compound, to obtainpressure-sensitive adhesive elastomers. Kelly (U.S. Pat. No. 3,330,797)discloses additional boron-containing self-adhering silicone elastomers.Foster (U.S. Pat. No. 3,379,607) added boron compounds to silicones topromote adhesion to surfaces. Proriol (U.S. Pat. No. 3,629,183)discloses boron-containing silicones that vulcanize to form adhesiveelastomers on heating. Greenlee (U.S. Pat. No. 3,772,240) found thatadding boric acid to silicones improved their adhesion to metals.Wegehaupt (U.S. Pat. No. 3,855,171) incorporates pyrogenically producedmixed oxides of boron and an element selected from the class consistingof silicon, aluminum, titanium and iron in silicones for the purposes ofpreparing either self-adhering elastomers or bouncing putty.

Maciejewski (U.S. Pat. No. 4,339,339) recognizes that bouncing putty'sbounciness makes it unable to absorb energy during sudden impacts. Hediscloses a boron-containing, non-vulcanizable silicone for use forhydrostatic damping and shock absorption that is able to absorb energyduring impacts because it does not exhibit the unusual resiliency ofbouncing putty.

SUMMARY OF THE INVENTION

The invention is directed to viscoelastic silicone rubber compositions,which are part of a broad class of compounds that include densematerials, foamed materials, comminuted materials, and materials thatcan be molded and even incorporated in other known materials to formblended materials and composite materials. These materials are solids inthat they have equilibrium shapes to which they return in the absence ofimposed stresses, but they exhibit time-dependent stiffnesses: they arestiffer at short timescales than they are at long timescales. Aviscoelastic silicone rubber composition of the invention exhibits aShore Hardness that decreases significantly as the duration of themeasurement increases. For example, as shown in FIG. 1 of InternationalPatent Application No. PCT/US2011/027720, which is incorporated hereinby reference, when a Shore durometer is pressed against the surface ofthe rubber, the immediate reading of the durometer is significantlygreater than the reading of that same durometer after it has been inplace for 60 seconds. In other words, a viscoelastic silicone rubbercomposition has a greater Shore Hardness at time zero, t=0, than it doesafter 60 seconds, t=60 seconds.

In one embodiment, the invention provides viscoelastic silicone rubbercompositions that exhibit a high level of resilience when subjected to asudden impact, but deform extensively when subjected to a prolongedstress. For example, a heavy metal ball dropped on the embodiment willrebound almost to its original height and leave the embodiment's shapevirtually unchanged. But that same heavy metal ball allowed to rest onthe embodiment for a minute or two will cause the embodiment's surfaceto dent significantly. When the ball is subsequently removed from theembodiment, the dent will gradually disappear from its surface and theembodiment will return to its original equilibrium shape.

Accordingly, in one embodiment, the viscoelastic silicone rubbers of theinvention are stiffer on short timescales than they are on longtimescales. When subjected to brief stresses, the viscoelastic siliconerubber composition is relatively stiff and elastic, and it resistschanging shapes. When subjected to sustained stresses, however, it isrelatively soft and accommodating, and it gradually changes shapes. Whenthose stresses are removed, it gradually returns to its original shape.These viscoelastic silicone rubbers resist compression set and they areextremely resilient in response to sudden impacts. They can be denserubbers, foam rubbers, and particles.

In one embodiment, the invention provides a silicone rubber compositionin which some of the crosslinks are permanent and others of thecrosslinks are temporary. Because a fraction of its crosslinks can comeapart and then reform, a viscoelastic silicone rubber composition of theinvention can relax stress in response to strain and thus adapt to newshapes. The composition has sufficient permanent crosslinks, however, toestablish a permanent equilibrium shape to which the composition willeventually return when not subject to any imposed stress. A viscoelasticsilicone rubber composition has sufficient temporary crosslinks to givethe composition a stiffness that is greater on short timescales than itis on longer timescales.

In another embodiment, the invention provides viscoelastic siliconerubber compositions comprising: (a) at least one polyorganosiloxanecomprising at least one ethylenically-unsaturated group; (b) optionallyat least one permanent crosslinking agent; and (c) at least onetemporary crosslinking agent; wherein the composition containssufficient permanent crosslinks to give the composition an equilibriumshape and sufficient temporary crosslinks to give the composition astiffness that is greater on short timescales than it is on longtimescales.

In another embodiment, the invention provides viscoelastic siliconerubber compositions comprising: (a) at least one branchedpolyorganosiloxane; (b) at least one permanent crosslinking agentpresent in an amount to provide sufficient permanent crosslinks to givethe composition an equilibrium shape; and (c) at least one temporarycrosslinking agent present in an amount to provide sufficient temporarycrosslinks to give the composition a stiffness that is greater on shorttimescales than it is on long timescales.

In another embodiment, the invention provides viscoelastic siliconerubber compositions comprising: (a) at least one polyorganosiloxane; (b)at least one permanent crosslinking agent present in an amount toprovide sufficient permanent crosslinks to give the composition anequilibrium shape; (c) at least one temporary crosslinking agent presentin an amount to provide sufficient temporary crosslinks to give thecomposition a stiffness that is greater on short timescales than it ison long timescales; and (d) at least one softening agent present in anamount sufficient to make the average lifetime of the temporarycrosslink of shorter duration than the average lifetime of the temporarycrosslink in the absence of the softening agent.

DESCRIPTION OF THE INVENTION

In one embodiment, the invention provides viscoelastic silicone rubber(VSR) compositions comprising: (a) at least one polyorganosiloxanecontaining at least one ethylenically-unsaturated group; (b) optionallyat least one permanent crosslinking agent; and (c) at least onetemporary crosslinking agent; wherein the composition containssufficient permanent crosslinks to give the composition an equilibriumshape and sufficient temporary crosslinks to give the composition astiffness that is greater on short timescales than it is on longtimescales. Each of these components is discussed below.

In another embodiment, this invention relates to viscoelastic siliconerubber compositions comprising: (a) at least one branchedpolyorganosiloxane; (b) at least one permanent crosslinking agentpresent in an amount to provide sufficient permanent crosslinks to givethe composition an equilibrium shape; and (c) at least one temporarycrosslinking agent present in an amount to provide sufficient temporarycrosslinks to give the composition a stiffness that is greater on shorttimescales than it is on long timescales. Each of these components isdiscussed below.

In another embodiment, the invention provides viscoelastic siliconerubber compositions comprising: (a) at least one polyorganosiloxane; (b)at least one permanent crosslinking agent present in an amount toprovide sufficient permanent crosslinks to give the composition anequilibrium shape; (c) at least one temporary crosslinking agent,present in an amount to provide sufficient temporary crosslinks to givethe composition a stiffness that is greater on short timescales than itis on long timescales; and (d) at least one softening agent present inan amount sufficient to make the average lifetime of the temporarycrosslink of shorter duration than the average lifetime of the temporarycrosslink in the absence of the softening agent. Each of thesecomponents is discussed below.

In a VSR composition of the invention, some of the crosslinks arepermanent and others of the crosslinks are temporary. Because a fractionof its crosslinks can come apart and then reform, a VSR composition ofthe invention can relax stress in response to strain and thus adapt tonew shapes. The composition has sufficient permanent crosslinks,however, to establish a permanent equilibrium shape to which thecomposition will eventually return when not subject to any imposedstress. In other words, the amount of permanent crosslinks is sufficientto make the rubber composition a solid. A VSR composition has sufficienttemporary crosslinks to give the composition a stiffness that is greateron short timescales than it is on longer timescales. If a force isquickly applied to a VSR composition of the invention, it feelsrelatively stiff and undergoes relatively little strain. If the force isapplied for a longer time, however, the composition feels relativelysoft and undergoes relatively substantial strain. Furthermore, thecomposition possesses a resilience during impact that increases with thespeed of that impact. When the composition is struck sharply, itexhibits enhanced stiffness and undergoes particularly little strain.Moreover, the composition stores the work done on its surfaceefficiently and returns nearly all of that work during the rebound.

Conventional silicone rubber is a solid formed when individualchain-like polyorganosiloxane molecules (silicones) are crosslinkedtogether into an extensive network. The crosslinks have little effect onthe short-range mobilities of the individual molecular chains sincethose chains can still slide across one another at room temperature.However, the crosslinks severely limit the long-range mobilities ofthose chains. The vast network of linkages, loops, and tangles presentin a heavily crosslinked silicone material give that material a fixedequilibrium shape and render it a solid.

Prior to crosslinking, a basematerial consisting of countless individualsilicone chains is liquid at room temperature, although it may be quiteviscous. In general, the higher the average molecular weight of theindividual silicone molecules, the more viscous the liquid. As theextent of crosslinking increases, the average molecular weight of theindividual silicone molecules increases and branching develops—three ormore silicone chains meeting at a single molecular junction. Loops andtangles also develop in the collection of crosslinked chains.

When the extent of crosslinking exceeds a certain level, the silicone“gels”—it becomes a soft, fragile solid. The network of crosslinkedsilicone chains is then so extensive that macroscopic regions of thematerial are spanned by crosslinked molecules and these molecules havelimited mobility. To form a robust silicone rubber, however,crosslinking must continue beyond the gel point. With additionalcrosslinking, the silicone rubber becomes stiffer and stronger, but italso becomes less able to adopt substantially different shapes. There isa trade-off between the crosslinked silicone's tendency to maintain aspecific equilibrium shape and its ability to adopt other shapes inresponse to stresses. Thus a highly crosslinked silicone rubber is verystiff and it resists deformation. When a silicone rubber is strainedbeyond its elastic limit, that rubber tears. To improve their tearstrengths, virtually all conventional silicone rubbers containreinforcing fillers such as fumed silica.

The VSR compositions of this invention are also crosslinked structuresbut differ from conventional silicone rubber compositions. The VSRcompositions of the invention include some crosslinks that are temporaryrather than permanent. In a conventional silicone rubber, all of thecrosslinks are permanent. A “permanent crosslink” is one that isunlikely to come apart at ordinary temperatures (generally <50° C.) inan ordinary amount of time (generally <1 day). One example of apermanent crosslink between two separate silicone chains is an-oxygen-silicon-oxygen-bridge that connects two silicon atoms inseparate silicone chains by way of another silicon atom. At ordinarytemperatures, the covalent chemical bonds that hold the-oxygen-silicon-oxygen-bridge together and link it to the two chains areextremely unlikely to come apart in an ordinary amount of time. Becauseall of its crosslinks are permanent, a fully cured conventional siliconerubber exhibits virtually no time evolution, e.g., deformation overtime. When subject to constant strain, a fully cured conventionalsilicone rubber responds with constant stress and acts to return itselfto its original equilibrium shape no matter how long that straincontinues. The relationship between stress and strain in a conventionalsilicone rubber resembles that of an ordinary spring and isapproximately time-independent.

In the VSR compositions of this invention, some crosslinks aretemporary. A “temporary crosslink” is a crosslink that has a significantprobability of coming apart at ordinary temperatures (<50° C.) in anordinary amount of time (<1 day). One example of a temporary crosslinkbetween two separate silicone chains is asilicon-oxygen-boron-oxygen-silicon bridge that connects two siliconatoms in separate silicone chains by way of the boron atom. Thesechemical bonds have a substantial probability of coming apart atordinary temperatures in an ordinary amount of time, particularly whenthere are water, alcohol, and/or carboxylic acid molecules present inthe material. Once a temporary crosslink has come apart, the boronmoiety becomes chemically active again and can attach itself to adifferent silicone chain or to the same silicone chain but after a timewhen the temporary crosslink has been broken. For simplicity, and merelyto illustrate this while not being bound to this theory, a temporarycrosslink can “open” (detach from one or more silicone chains) and“close” (attach to one or more silicone chains) in a relatively shortamount of time (e.g., in milliseconds, seconds, minutes, or hours). Therate at which the temporary crosslinks open and close may depend ontemperature and the chemical environment near those crosslinks.

Because some of its crosslinks are temporary, a fully cured VSR of thisinvention exhibits time evolution. When subject to a strain that appearssuddenly and then remains constant, the material initially responds withconstant stress. On short timescales, the material's stiffness dependson both the permanent and temporary crosslinks. But as the material'stemporary crosslinks open and close, its network structure evolves andits stress relaxes. At long time scales, in the limit of infinite time,the temporary crosslinks relax completely and thus do not contribute tothe material's stress. Since the permanent crosslinks cannot relax, theycontinue to contribute to the material's stress indefinitely. On longtimescales, the material's stiffness and shape depend only on thepermanent crosslinks.

The temporary crosslinks remain important in the strained but relaxedVSR. The temporary crosslinks do not simply open during the relaxationprocess; they close to form new and different temporary crosslinks. Whenthe strain is suddenly removed from the material, the formation of newtemporary crosslinks produces stress in the material. In effect, thestrained material gradually adapted to its new strained shape and itacts to oppose a sudden return to its original equilibrium shape. Thisnew stress gradually relaxes as the temporary crosslinks open and close,until, over a long time scale, in the limit of infinite time, theunstrained material becomes once again free of stress and returns to itsoriginal shape.

It is useful to view a VSR of this invention as having two overlappingand possibly interconnected networks: one permanent and the othertemporary. The permanent network has a fixed topology and gives thematerial a permanent equilibrium shape—the shape to which it will returnwhen free of imposed stress for a sufficient period of time. When thematerial is subject to constant strain, that permanent network producesa constant stress. The temporary network, however, has a topology thatevolves with time and it relaxes so as to eliminate stress.

When a VSR has been free of strain for a sufficient time, the materialadopts its equilibrium shape and both of the permanent and temporarynetworks are free of stress. The overall material is then free of bothstress and strain.

VSR compositions of the invention exhibit time-dependent responses tosudden changes in strain. When an unstressed, unstrained VSR compositionof the invention is subject to a sudden strain which then remainsconstant, its permanent crosslink network responds with a stress thatrises suddenly and then remains constant. In contrast, the material'stemporary network responds with a stress that rises suddenly and thenrelaxes, ultimately to zero. When the strained but relaxed material issuddenly returned to zero strain and then remains at zero strain, itspermanent network responds with stress that drops suddenly to zero andremains at zero. The material's temporary network, however, respondsonce more with a stress that rises suddenly and then relaxes to zero. Inother words, the permanent network acts to return the material to itsequilibrium shape while the temporary network acts to oppose any rapidchange in the material's shape.

VSR compositions of the invention also exhibit time-dependent responsesto sudden changes in stress. When an unstressed, unstrained VSRcomposition of the invention is subject to a sudden stress that thenremains constant, both its permanent and temporary network oppose thestress and the material responds with a small strain. The temporarynetwork, however, gradually relaxes its opposition to the stress so thatthe material's strain increases with time. Eventually, only thepermanent network is opposing the stress and the material reaches aconstant large strain.

When the stressed but relaxed material is suddenly returned to zerostress and then remains at zero stress, the two networks oppose oneanother. The permanent network acts to return the material to itsequilibrium shape, but the temporary network has adapted to the newshape and acts to oppose the return to material's equilibrium shape. Thetemporary network, once more, gradually relaxes (the temporarycrosslinks open and reform) its opposition and allows the material toreturn to its equilibrium shape.

To be a solid (i.e., to have a permanent equilibrium shape), anysilicone rubber must have enough permanent crosslinks to connect theindividual silicone chains into macroscopic networks, so that topologyand tangles forever dictate that material's shape. The VSR compositionsof this invention are no exception: they must have sufficient permanentcrosslinks to establish a permanent equilibrium shape. The VSRcompositions of the invention may be formed into a wide variety ofshapes and using the same techniques as with conventional siliconerubbers. Typically, as is known in the art, a silicone rubber is shapedby placing an uncured liquid silicone composition into a mold and thencrosslinking that composition into a solid rubber.

Once a minimum amount of permanent crosslinking has been reached,however, additional crosslinks in a VSR composition of the invention mayinclude further permanent crosslinks or may be all temporary crosslinks.Additional permanent crosslinks increase both the short timescale andlong timescale stiffnesses of the silicone rubber, while additionaltemporary crosslinks increase only the short timescale stiffnes of a VSRcomposition of the invention.

One common approach to forming crosslinks is to add a crosslinkingagent, often in the presence of one or more catalysts. Catalysts mayalso assist in the self-crosslinking between crosslinkable groups on thepolyorganosiloxane, without the addition of a crosslinking agent.Molecules of the crosslinking agent then attach themselves to one ormore of the silicone chains. A crosslinking molecule that attachesitself to only a single chain does little to form extended networks.Even a crosslinking molecule that attaches itself to two chains barelycontributes to network forming. But a crosslinking molecule thatattaches itself to three or more chains contributes significantly to thevast networks needed to form solids.

The amount of crosslinking agent needed to transform a liquid siliconeinto a solid gel has been determined theoretically by Flory (Paul J.Flory, J. Phys. Chem. 46, 132 (1942)), Stockmayer (Walter H. Stockmayer,J. Chem. Phys. 11, 45 (1943)), and others. For the case where thecrosslinking agent attaches itself only to the ends of the siliconechains, this threshold amount follows a simple formula. The term“coordination number” denotes the number of silicone chain ends to whicha single molecule of the crosslinking agent can bind and it is assumedthat the crosslinking agent attaches itself to chain ends with perfectefficiency—i.e., that the number of attached chain ends is equal to thenumber of crosslinker molecules times the crosslinker's coordinationnumber. In that case, the gelation threshold is:

$\frac{{attached}\mspace{14mu}{chain}\mspace{14mu}{ends}}{{total}\mspace{14mu}{chain}\mspace{14mu}{ends}} = \frac{1}{\left( {{{coordination}\mspace{14mu}{number}} - 1} \right)}$

For a crosslinking agent that attaches to 3 chains, at least one half ofthe chain ends must be attached to crosslinking molecules before thematerial can begin to solidify. For a crosslinking agent that attachesto 4 chains, one third of the chain ends must be attached. And for acrosslinking agent that attaches to 21 chains, only 5% of the chain endsmust be attached in order for the material to begin to solidify.

It is clear that a liquid composed of silicone chains can be transformedinto a solid by attaching a small fraction of the chains' reactive endsto a crosslinking agent with a large coordination number. If thiscrosslinking agent forms permanent crosslinks, then it will give thematerial a permanent equilibrium shape. The remaining reactive chainends are still available for attachment to something else, such as atemporary crosslinking agent.

The crosslinking agent may also attach itself to points along thebackbones of the silicone chains and/or to branch points in branchedsilicone molecules. However, it is more difficult to predict the amountof crosslinking agent needed to transform a liquid silicone into a solidgel under such conditions. Nonetheless, once that crosslinking agent hasformed enough permanent crosslinks to give the material a permanentequilibrium shape, any remaining reactive sites on the siliconemolecules can be attached to something else, such as a temporarycrosslinking agent.

Polyorganosiloxanes

Any polyorganosiloxane having silanol groups at the ends ofpolyorganosiloxane chains and/or on the backbones of polyorganosiloxanechains may be used to prepare a VSR composition of the invention,including, for example, silanol-terminated polyorganosiloxanes (STPOS).Polyorganosiloxanes generally exist as liquids of varying viscosities.Those liquids may be used as the base material for the preparation of aVSR composition of the invention or as the base material for thepreparation of partially-crosslinked, branched polyorganosiloxanes thatmay also be used for the preparation of a VSR composition of theinvention. “Branched polyorganosiloxanes” includes thosepolyorganosiloxanes that have one or more branch points and/or aremixtures thereof.

The polyorganosiloxane base which may be used to prepare the VSRcompositions (or partially-crosslinked, branched polyorganosiloxanes)are preferably those polyorganosiloxane polymers having primarily methylgroups bound to the silicon atoms making up the siloxane backbone withhydroxyl groups at the terminal ends of the siloxane backbone. The baseis typically a liquid polymer composition. The molecular weight of thepolymers may range from about 400 to about 110,000 Daltons andpreferably from about 700 to about 43,500 Daltons and more preferablyfrom about 1,600 to about 36,000 Daltons. The viscosity of the polymersmay range from about 16 to about 50,000 cSt and preferably from about 30to 3,500 cSt and more preferably from about 40 to about 2000 cSt. STPOS,particularly silanol-terminated polydimethylsiloxane (STPDMS), arecommonly used in condensation-cure silicone rubbers and in thepreparation of ordinary borosilicones. Each STPOS molecule has twosilanol groups, one at each end. Preferred STPOS polymers include:silanol-terminated polydimethylsiloxanes, formula (I);silanol-terminated diphenylsiloxane-dimethylsiloxane copolymers, formula(II); and silanol-terminated poly trifluoropropylmethylsiloxanes,formula (III). These preferred STPOS are available from Gelest, Inc. andfrom Emerald Performance Materials.

In formulas (I), (II), and (III), the variables “m” and “n” are both 1or greater and represent the number of the repeating units inparentheses to give the molecular weight of the particular polymer.Preferred STPOS are those of formula (I), particularly those availablefrom Gelest Inc. identified in Table 1 below, and from EmeraldPerformance Materials indentified in Table 2 below.

TABLE 1 Gelest Viscosity Molecular Code (cSt) Weight % (OH) (OH)-Eq/kgDMS-S12 16-32 400-700 4.5-7.5 2.3-3.5 DMS-S14 35-45  700-1500 3.0-4.01.7-2.3 DMS-S15 45-85 2000-3500 0.9-1.2 0.53-0.70 DMS-S21  90-120 42000.8-0.9 0.47-0.53 DMS-S27 700-800 18,000 0.2 0.11-0.13 DMS-S31 100026,000 0.1 0.055-0.060 DMS-S32 2000 36,000 0.09 0.050-0.055 DMS-S33 350043,500 0.08 0.045-0.050 DMS-S35 5000 49,000 0.07 0.039-0.043

TABLE 2 Emerald Viscosity Code (cSt) SFR 70 70 SFR 100 100 SFR 750 750SFR 2000 2,000

Partial crosslinking of these polyorganosiloxanes, including, forexample, STPDMS fluids, can produce fluids containing branched siloxanemolecules that have 3, 4, 5, or more terminal silanols. These partiallycrosslinked siloxane fluids can also contain backbone silanols ofcoordination number 3 or 4, which may be used herein to bind togethersiloxane chains to form T-branches:. . . —O—Si(CH₃)(—PDMS—OH)—O— . . .Q-branches:. . . —O—Si(—PDMS—OH)₂—O— . . .and backbone silanol groups (via hydrolysis of the crosslinking agent):. . . —O—Si(CH₃)(OH)—O— . . .and. . . —O—Si(OH)₂—O— . . .

The extent of the partial crosslinking that occurs depends on the amountof crosslinking agent used, the presence or absence of crosslinkablegroups in the polyorganosiloxane (e.g., the silanol groups and theethylenically-unsaturated groups), the temperature at which the partialcrosslinking occurs, the time allowed for partial crosslinking, themoisture content of the mixture, and the presence or absence ofcatalyst(s) during partial crosslinking. Partial crosslinking in thepresence of moisture encourages the formation of some backbone silanolgroups whereas partial crosslinking in the absence of moisture (i.e., incarefully dried materials) encourages the formation of branches.

Partial crosslinking increases the viscosity of the silicone fluidsignificantly. The viscosity increases gradually as molecules having twocrosslinked STPDMS chains form in the fluid. But as larger crosslinkedmolecules (3, 4, 5, or more STPDMS chain's) become common, the fluid'sviscosity increases dramatically. Partially crosslinked STPDMS fluidsbecome extraordinarily viscous fluids well before they cross thegelation threshold to form true solids. By controlling the amount ofcrosslinking agent and the conditions under which crosslinking takesplace, partially crosslinked STPDMS fluids can be formed withviscosities ranging from less than 2 times that of the original STPDMSfluid to 1000 or more times that of the original STPDMS fluid. Partiallycrosslinked STPDMS fluids/semisolids/solids may also be formed in theregimes below, at, and above the gelation threshold.

In another embodiment of the invention, branched polyorganosiloxanes maybe formed containing both silanol groups and ethylenically-unsaturatedgroups, such as, for example, vinyl groups by using, for example,vinyltriacetoxysilane (VTAS), vinyltrimethoxysilane,vinyltrichlorosilane, and/or vinyltriethoxysilane (VTEOS) ascrosslinking agents to partially crosslink STPDMS molecules. Thispartial crosslinking places a vinyl group at each T-branch or backbonesilanol group. VTAS is particularly useful for this purpose because itcrosslinks STPDMS quickly and without the need for a catalyst,especially at temperatures of 60° C. or more. When the STPDMS has beencarefully dried, partial crosslinking with VTAS can produce branchedpolyorganosiloxanes with multiple terminal silanols. Using thesetechniques, silicone fluids, semisolids, and solids that have bothsilanol groups and ethylenically-unsaturated groups, such as, forexample, vinyl groups, on their molecules may be formed.Ethylenically-unsaturated groups include any unsaturated chemicalcompound containing at least one carbon-to-carbon double bond (e.g.,alkenyl groups, vinyl groups, vinylidene groups, allyl groups, acrylategroups, methacrylate groups, etc.). U.S. Pat. Nos. 4,360,610 and5,674,935, the disclosures of which are incorporated by reference,disclose exemplary structures of and methods of makingsilanol-terminated polyorganosiloxanes containingethylenically-unsaturated (i.e., vinyl) groups, which may be used in theinvention.

The ethylenically-unsaturated group content of the polyorganosiloxanemay range from about 0.01 wt % to about 5.0 wt %, preferably from about0.02 wt % to about 1.0 wt %, and most preferably from about 0.04 wt % toabout 0.85 wt %, by weight of the polyorganosiloxane. The silanolcontent of the polyorganosiloxarie may range from about 0.03 wt % toabout 7.5 wt %, preferably from about 0.08 wt % to about 4.0 wt %, andmost preferably from about 0.09 wt % to about 2.5 wt %, by weight of thepolyorganosiloxane.

Partial crosslinking with VTAS proceeds quickly at temperatures of 100°C. or more. Above 100° C., the approximate boiling point of water at sealevel, water is able to escape from the silicone fluid rapidly asbubbles of vapor. Partial crosslinking with VTAS proceeds even morequickly at temperatures of 118° C. or more. Above 118° C., theapproximate boiling point of acetic acid at sea level, acetic acid isable to escape from the silicone fluid rapidly as bubbles of vapor.Partially crosslinking with VTAS proceeds especially quickly attemperatures of 160° C. or more. See, e.g., Examples 68-73. Preferably,the partial crosslinking with VTAS is done at temperatures ranging fromabout 125 to 140° C. See, e.g., Examples 74-77.

The viscosity of a partially-crosslinked STPDMS silicone fluid can beincreased by the addition of a catalyst(s) and/or other agent(s) thatfacilitates homocondensation of silanol groups. Because homocondensationof silanol groups reduces the number of silanol groups remaining in thefluid, it increases the effective fraction of crosslinks of the fluidand causes the fluid to approach or even exceed the gelation threshold.

Homocondensation of silanol groups:HO—PDMS₁—OH+HO—PDMS₂—OH″HO—PDMS₁—O—PDMS₂—OH+H₂Ocan facilitate the formation of the networks present in a VSRcomposition of the invention. By reducing the total number of silanolgroups and therefore the total chain ends, that homocondensation processeffectively increases the ratio of attached chain ends to total chainends and increases the level of the network-formation in the VSR. Thishomocondensation process can alter a partially crosslinked network thatis below the gelation threshold and therefore a liquid, so that thatnetwork is above the gelation threshold and therefore a solid.

Because it raises the level of network formation inpartially-crosslinked silicones, homocondensation of silanol groups cancontribute significantly to the curing and solidification of a VSR ofthe invention. When a crosslinking agent binds to silanol groups, theamount of that crosslinker can be specified in terms of the percent ofinitially available silanol groups use to form its crosslinks. 100% ofthat crosslinker is thus the amount necessary to use all of theinitially available silanols—it saturates the silanol. For example, aVSR that originally contains 45% methyltriethoxysilane (MTEOS) and 35%trimethylborate (TMB) is seemingly under-saturated and might be expectedto retain 20% of its original silanol groups in their unreacted form. Itmight also be expected to be a liquid, since 50% MTEOS is required toreach the gelation threshold. However, homocondensation of silanolsgroups, usually expedited by a catalyst, can eliminate 20% of theoriginal silanol groups so that the resulting VSR is fully saturated.Moreover, its effective MTEOS saturation is then 56%, exceeding thegelation threshold and rendering it a solid. See, e.g., Examples 37 and52-60.

Sulfuric acid, even in minute amounts and even at room temperature,encourages the homocondensation of silanol groups inpartially-crosslinked STPDMS silicone fluids. Removal of the watermolecules released by homocondensation further encourageshomocondensation. Homocondensation can be terminated by removing orneutralizing the sulfuric acid. See, e.g., Examples 62-67.

Vacuum degassing of a partially-crosslinked STPDMS silicone fluidcontaining sulfuric acid causes the homocondensation process to proceedmore rapidly. By removing accumulated water molecules, that vacuumdegassing shifts the equilibrium distribution of silicone molecules inthe fluid toward higher molecular weight. See, e.g., Examples 62, 64,and 65.

Permanent Crosslinking Agents

One general embodiment of this invention is the combination of at leastone linear and/or branched polyorganosiloxane with two differentcrosslinking agents—a permanent crosslinking agent and a temporarycrosslinking agent. The permanent crosslinking agent forms permanentsiloxane and/or carbon crosslinks with the polymers in thepolyorganosiloxane. The temporary crosslinking agent forms temporarycrosslinks with that same polyorganosiloxane. In a VSR composition ofthe invention, there must be sufficient permanent crosslinking agentpresent to establish a robust permanent network and give the rubbercomposition its permanent equilibrium shape. The amount of temporarycrosslinking agent may be varied.

In VSR compositions of the invention, a permanent crosslink can be anychemical linkage that permanently connects polyorganosiloxane chainsegments (although a linkage that simply joins two chain segments sothat they form a single longer chain segment is a “chain extension”rather than a true crosslink). The conventional curingmechanisms—condensation cure, addition cure, and peroxide cure—all formsuch chemical linkages between chain segments. Additionally, thebranched polyorganosiloxanes effectively have a pre-existing crosslinkwherever three or more chain segments meet at a branch point.

The invention can make use of any permanent crosslinking technique ormethod known in the prior art. In particular, it can make use ofcondensation-cure crosslinking, addition-cure crosslinking, peroxidecrosslinking, as well as other known organo-silicone chemistries,including cures based on isocyanates and epoxies (see, e.g., Examples26-28, 33-35, 37, and 48).

The permanent crosslinks needed to give a VSR its equilibrium shape andrender it a solid can be any of the known crosslinks betweenpolyorganosiloxanes, including siloxane bridges (chain-O—Si—O-chain) andcarbon bridges (chain-C-chain, -chain-C—C-chain, chain-C—C—C-chain,etc.). While VSR compositions of the invention based on the condensationcure generally rely on siloxane bridges for permanent crosslinks, VSRcompositions of the invention based on the addition cure and on theperoxide cure frequently rely on carbon bridges for permanentcrosslinks. See, e.g., Examples 26-28 and 33-35.

The siloxane and carbon bond-forming crosslinking agent may be anycrosslinking agent known in the art to crosslink polyorganosiloxanes.Depending on the type of cure used (e.g., condensation, addition,peroxide), for example, one of skill in the art would readily know whichpermanent crosslinking agent is suitable for creating permanentcrosslinks. Suitable siloxane bond-forming crosslinking agents include,for example, polydiethoxysilane (PDEOS), polydimethoxysilane,tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), MTEOS,methyltrimethoxysilane, tetra-n-propoxysilane, vinyltriacetoxysilane(VTAS), methyltriacetoxysilane, ethyltriacetoxysilane,tetrakis(methoxyethoxy)silane, vinyltrichlorosilane,methyltrichlorosilane, ethyltrichlorosilane, tetrachlorosilane,polymethylhydrosiloxane (PMHS),methylhydrosiloxane-dimethylhydrosiloxane copolymer (PMHS-PDMS),hydride-terminated polymethylhydrosiloxane, and hydride-terminatedmethylhydrosiloxane-dimethylhydrosiloxane copolymer. Siloxanebond-forming crosslinking agents are available from Gelest, Inc.,Sigma-Aldrich, Alfa-Aesar, and Emerald Performance Materials. Suitablecarbon bond-forming crosslinking agents include, for example,polymethylhydrosiloxane (PMHS),methylhydrosiloxane-dimethylhydrosiloxane copolymer (PMHS-PDMS),hydride-terminated polymethylhydrosiloxane, hydride-terminatedmethylhydrosiloxane-dimethylhydrosiloxane copolymer, benzoyl peroxide,2,4-dichlorobenzoyl peroxide (DCBP), dicumyl peroxide (DCP), and2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (VX). Carbon-bond-formingagents are available from Gelest, Inc., Sigma-Aldrich, Alfa-Aesar,Arkema, Inc., and Emerald Performance Materials. The amount of aparticular siloxane and/or carbon bond-forming crosslinking agent useddepends upon the number of functional groups within the crosslinkingagent. The amount of the crosslinking agent must be sufficient to yielda permanent equilibrium shape but generally in less than the amountsufficient to react with all of the silanol and carbon groups, so thatsome silanol and carbon groups are available to form temporarycrosslinks. The permanent crosslinking agent may be present in the VSRcompositions of the invention in an amount ranging from about 0.02 wt %to 20.0 wt %, such as, for example, from about 0.04 wt % to about 15.0wt %, such as, for example, from about 0.08 wt % to about 8.0 wt %,based on the total weight of the VSR composition. Preferably, thepermanent crosslinking agent may be present in the VSR compositions ofthe invention in an amount ranging from about 0.1 wt % to about 5.0 wt%, based on the total weight of the VSR composition.

In another embodiment, the permanent crosslinks need not be formed usinga permanent crosslinking agent. Rather, some or all of the permanentcrosslinks creating chemical linkages that permanently connectpolyorganosiloxane chain segments may be formed through means other thana permanent crosslinking agent. The permanent crosslinks may be createdthrough the presence of at least one permanent crosslinkable grouppresent in the polyorganosiloxane, such as, for example, apolyorganosiloxane comprising at least one ethylenically-unsaturatedgroup. In the peroxide cure, for example, a free radical may attack thecarbon-carbon double bond in the ethylenically-unsaturated group andcause those carbons to grab onto another polyorganosiloxane chain (e.g.,via self-crosslinking). Alternatively, any process applied to thepolyorganosiloxanes that creates permanent crosslinks between thepolyorganosiloxane chains may be used to make some or all of thepermanent crosslinks. For example, the application of anyelectromagnetic radiation (e.g., microwave, near infrared, ultraviolet,x-ray, gamma rays, high-energy gamma rays, etc.) may cause permanentcrosslinks to form between some polyorganosiloxanes. Any catalyst thatcauses the polyorganosiloxanes to form permanent crosslinks, such as,for example, platinum; may be used to make some or all of the permanentcrosslinks.

Any combination of the above-mentioned means for creating permanentcrosslinks between polyorganosiloxane chains may be used in theinvention. Thus, any permanent crosslinking agent, crosslinkable grouppresent in the polyorganosiloxane, process, or catalyst that producespermanent crosslinks between polyorganosiloxanes to give the material apermanent equilibrium shape may be used.

Temporary Crosslinking Agents

In a VSR composition of the invention, a temporary crosslink can be anychemical linkage that temporarily connects polyorganosiloxane chainsegments. Temporary crosslinking agents may be based on boron, tin,titanium, aluminum, zirconium, arsenic, lead, and phosphorous atoms. Inparticular, linkages that can serve as temporary crosslinks in VSRcompositions of the invention include, but are not limited to,-oxygen-boron-oxygen-bridges, -oxygen-titanium-oxygen-bridges, and-oxygen-aluminum-oxygen-bridges.

In a VSR composition of the invention, at least one boron-containingcompound is present in an amount to provide sufficient temporarycrosslinks to give the composition a resilience during impact thatincreases with the speed of that impact. In another VSR composition ofthe invention, the composition comprises at least about 0.1 wt % of atleast one boron-containing compound and exhibits a stiffness that isgreater on short timescales than it is on long timescales and aresilience during impact that increases with the speed of that impact.

The boron-containing crosslinking agent may be, for example, boric acid(BA) or a boric acid ester such as TMB, triethyl borate (TEB),triisopropyl borate (TIB), and tributyl borate. Due to their chemicalstructure, boron-containing crosslinking agents have three functionalgroups by which to react with the silanol groups in thepolyorganosiloxane. The use of a boron compound as the temporarycrosslinking agent has an additional consequence: this materialembodiment of the invention typically exhibits a remarkably highstiffness and resiliency in response to sudden impacts.

In one embodiment, the branched polyorganosiloxanes having more than twosilanol groups can combine with boron compounds to form novelborosilicones, titanium compounds to form novel titanosilicones,aluminum compounds to form novel aluminosilicones, or mixtures thereof(e.g., borotitanosilicones). Borosilicones of the invention, forexample, are less soluble in alcohols and other solvents than ordinarySTPDMS-based borosilicones and that they retain their viscoelasticproperties better than do ordinary borosilicones when exposed tomoisture or liquid water.

When adding silanol groups to a STPDMS chain, each silanol group can beplaced along the backbone of the polydimethylsiloxane (PDMS) chain:. . . —O—Si(CH₃)(OH)—O— . . .or as a terminal silanol on a branching PDMS chain segment:. . . —O—Si(CH₃)(—PDMS—OH)—O— . . .

Both types of additional silanol groups contribute to the bonding ofborosilicones. Branched PDMS molecules that have 3, 4, 5, or moreterminal silanols can combine with boron compounds to form novelborosilicones having greater tensile strengths and more resistance tosolvents than ordinary STPDMS-based borosilicones.

In another embodiment, a wide range of linear and/or branchedpolyorganosiloxanes having silanol groups and ethylenically-unsaturatedgroups on some, most, or all of their molecules can be combined with awide range of boron compounds to form vulcanizableborosilicones—borosilicone compounds that can be vulcanized (i.e.,permanently crosslinked to form solids). In addition topartially-crosslinked STPDMS fluids, a more general class ofpolyorganosiloxanes having both ethylenically-unsaturated groups andsilanol groups along their backbones and/or at their chain-ends could besynthesized by persons knowledgeable in the art. Such molecules may belinear or branched and they could have the ethylenically-unsaturated andsilanol groups distributed in many different ways. Borosilicones formedfrom these polyorganosiloxanes may be turned into VSR compositions ofthe invention via, for example, the peroxide cure, the addition cure atroom temperature, and the addition cure at elevated temperature.

Vulcanizable partially crosslinked borosilicones (VPCBs) may be preparedfrom silanol-containing, partially-crosslinked, branched STPDMSsilicones containing ethylenically-unsaturated groups by reacting themwith, for example, trimethyl borate (TMB). These borosilicones may bevulcanized to form VSR compositions of the invention via, for example,the peroxide cure, the addition cure at room temperature, and theaddition cure at elevated temperature.

As discussed below, the vulcanizable borosilicones may also be combinedwith many other materials prior to vulcanization, notably withreinforcing fillers (e.g., hexamethyldisilazane-treated fume silica(TFS) and Garamite 1958 (G1958)), with conventional methyl vinylsilicone fluids and/or high-temperature vulcanizing silicones (HCRsilicones) (e.g., Wacker R401/50), and with conventional STPDMS-basedborosilicones (e.g., 100% TMB in 90-120 cSt STPDMS), as well as withcombinations thereof. VSRs of the invention may be formed from thosecombinations. These blended materials vulcanize to form VSRs of theinvention with excellent properties. Adding HCR silicone can greatlyincrease the maximum elongation, tear resistance, and tensile strengthof the resulting VSR. Adding up to 25 wt % or more conventionalSTPDMS-based borosilicones accentuates the difference between the shorttimescale stiffness and long timescale stiffness of the resulting VSR.

In another embodiment, borosilicones and vinyl-methyl silicone fluidsand/or HCR silicones can be blended together and then vulcanized, usingeither the peroxide cure or the addition cure, to produce VSRs of theinvention. The vinyl-methyl silicone fluids and/or HCR silicones shouldbe at least 10 weight percent of the blend and preferably at least 25weight percent of the blend. The resulting VSRs of the invention havelarge elongations at break and are relatively resistant to tearing. See,e.g., Examples 7-13 and 41-43.

In addition, blends of branched borosilicones with vinyl-methyl siliconefluids and/or HCR silicones can be vulcanized by the addition cure orthe peroxide cure combined with the condensation cure. See, e.g.,Example 45. These blends can also be vulcanized into foamed VSR of theinvention, using any of the known techniques for making foamed siliconerubbers and viscoelastic silicone rubbers. See, e.g., Example 44.

Blends of (a) branched borosilicones, titanosilicones, aluminosilicones,and/or mixtures thereof (e.g., borotitanosilicones) and (b) conventionalvulcanizable silicones such as HCR compositions and methyl-vinylsilicone fluids can be vulcanized to produce VSR of the invention. VSRof the invention may be prepared from these pairings using both theperoxide cure (e.g., with 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane(Luperox® 101) crosslinker and heat) and the addition cure (e.g., withpolymethylhydrosiloxane crosslinkers and Pt-complex).

A borosilicone formed from branched polyorganosiloxanes with more thantwo silanol groups on some, most, or all of their molecules can bevulcanized via the condensation reaction. When suitable catalyst(s)and/or suitable crosslinking agent(s) are added to the borosilicone,remaining silanol groups in the borosilicone as well as silanol groupsformed via hydrolysis of -oxygen-boron-oxygen-bridges can condense toform permanent -oxygen-silicon-oxygen-linkages.

A partially-crosslinked borosilicone fluid (a close relative to a VSR inwhich the permanent network is not quite extensive enough to give thecomposition a permanent equilibrium shape) can be transformed into a VSRthrough homocondensation of silanol groups. Generally, thishomocondensation is initiated by the addition of a catalyst and may ormay not be accompanied by a crosslinking agent. For example, adding AMA(AeroMarine Silicone Accelerator) to a borosilicone based on partiallycrosslinked STPDMS can cause that borosilicone to solidify into a VSR.See, e.g., Example 37.

Titanium and/or aluminum compounds can substitute for some or all of theboron compounds as temporary crosslinkers in VSR compositions of theinvention. VSR of the invention using titanium compounds (e.g., atitanium alkoxides, such as titanium isopropoxide (TIP), titaniumbutoxide, titanium methoxide, titanium ethoxide, and titanium propoxide,titanium dibutoxide(bis-2,4-pentanedionate), titaniumdiisopropoxide(bis-2,4-pentanedionate), titaniumdiisopropoxide(bis-ethylacetoacetate), titanium 2-ethylhexoxide,titanium trimetylsiloxide, polydibutyltitanate, anddiethoxysiloxane-ethyltitanate copolymer) and/or aluminum compounds(e.g., aluminum alkoxides, such as aluminum propoxide, aluminumisopropoxide, aluminum butoxide, aluminum methoxide, and aluminumethoxide, and diethoxysiloxane-butylaluminate copolymer) as temporarycrosslinkers may be made as well as VSRs using mixtures of boron,titanium, and/or aluminum compounds as temporary crosslinkers. Ingeneral, any borosilicone or VSR based on boron can also be formulatedusing titanium and/or aluminum in place of some or all of the boron inthat material. For example, titanium bridges (chain-O—Ti—O-chain) and/oraluminum bridges (chain-O—Al—O-chain) can act as temporary crosslinksbetween polyorganosiloxanes and these titanium and/or aluminum bridgescan replace some or all of the boron bridges (chain-O—B—O-chain) in VSRof the invention. See, e.g., Example 14 and 15.

A VSR composition of the invention contains both permanent and temporarycrosslinks. For the permanent crosslinking agent, the minimum amount ofcrosslinking is set by the need to exceed the gelation threshold. Forthe temporary crosslinking agent, however, the minimum amount is setonly by the desired degree of temporary crosslinking. It is preferablefor the temporary crosslinking agent, possibly assisted by the permanentcrosslinking agent, to use approximately 100% of the silanol groups onthe polyorganosiloxane—that is, to reach approximately 100% saturationof the silanol groups. That amount is generally at least 0.005 wt %, orat least 0.1 wt %. Greater amounts of temporary crosslinking agents maybe used and depend upon the composition and properties desired for theparticular VSR composition. The temporary crosslinking agent may bepresent in the VSR compositions of the invention in an amount rangingfrom about 0.01 wt % to 20.0 wt %, such as, for example, from about 0.05wt % to about 15.0 wt %, such as, for example, from about 0.08 wt % toabout 12.0 wt %, based on the total weight of the VSR composition.Preferably, the temporary crosslinking agent may be present in the VSRcompositions of the invention in an amount ranging from about 0.1 wt %to about 11.0 wt %, and, more preferably, from about 0.3 wt % to about2.5 wt %, based on the total weight of the VSR composition.

Softening Agents

The temporary crosslinks, for example, the boron crosslinks(-oxygen-boron-oxygen-bridges), between branched polyorganosiloxanes inVSR compositions of the invention can be extremely long-lived in theabsence of reactive chemicals or chemical groups in the temporarycrosslinker-silicone composition (e.g., boron-silicone composition). Forexample, an extremely pure borosilicone composition—one that isessentially free of moisture, alcohols, carboxylic acids, and silanolgroups—exhibits behavior that is difficult to distinguish from that of aconventionally crosslinked silicone composition when studied onrelatively short timescales, such as seconds, minutes, hours, or evenlonger, near room temperature.

When there is a complete absence of chemicals that can react with andthereby open boron bridges (chain-oxygen-boron-oxygen-chain), theboron-based crosslinks in VSR compositions of the invention areeffectively permanent near room temperature. Without suchboron-bridge-opening-chemicals, the boron linkages rarely open near roomtemperature. Therefore, VSR compositions of the invention that areapproximately devoid of those chemicals are approximately elastic(rather than viscoelastic) on timescales of 1 minute or less. See, e.g.,Examples 48 and 59. Elevated temperatures (e.g., 160° C. or greater),however, can soften these borosilicones, i.e., open the boron linkages.

If chemicals (i.e., softening agents) that can open a boron bridge(chain-oxygen-boron-oxygen-chain) are present, the boron-basedcrosslinks in VSR compositions of the invention are effectivelytemporary near room temperature. Such boron-bridge-opening-chemicalsinclude, but are not limited to, water, alcohols, polyols, silanols, andcarboxylic acids. See, e.g., Examples 1-13, 48, and 60. Thus, in oneembodiment, the VSR compositions of the invention may comprise at leastone softening agent present in an amount sufficient to make the averagelifetime of the temporary crosslink of shorter duration than the averagelifetime of the temporary crosslink in the absence of the softeningagent.

Including softening agents that are reactive with the temporarycrosslinks, such as, for example, boron crosslinks, (e.g., moisture,alcohols, carboxylic acids, and unreacted silanol groups) in a VSRcomposition hastens stress relaxation in that composition. Those addedchemicals soften the VSR on timescales that are sensitive to the rate atwhich the temporary crosslinks open. At the very shortest timescales,the temporary crosslinks are so unlikely to open that there is littleopening-rate sensitivity. At the very longest timescales, the temporarycrosslinks are so likely to open that there is again little opening-ratesensitivity. But at intermediate timescales, wherein the temporarycrosslinks may or may not open to relax stress, increasing the openingrate with chemicals will increase the probability of stress relaxationand thereby soften the composition.

For VSR compositions of the invention to exhibit significantviscoelasticity on timescales of 1 minute or less, those materialsgenerally should contain boron-bridge-opening-chemicals so that thoseboron-based crosslinks behave as temporary crosslinks. Thoseboron-bridge-opening-chemicals may be added explicitly to the VSRcompositions of the invention, before, during, or after curing. Thoseboron-bridge-opening softening agents may also be present naturally inthe original chemicals used to form the VSR compositions of theinvention, as impurities or additives in those chemicals, as reaction ordecay products, or in the environments to which the VSR compositions ofthe invention are exposed. See, e.g., Examples 1-13, 48, and 60.

Chemicals bearing hydroxyl and carboxyl groups are particularlyeffective boron-bridge-opening-chemicals. Water, alcohols, polyols,silanols, and carboxylic acids are examples of chemicals bearinghydroxyl and carboxyl groups. See, e.g., Examples 1-13, 48, and 60. Forexample, alkyl alcohols, alkenyl alcohols, polyalkenyl alcohols, arylalcohols, monols, diols, and triols, each of which containing from 1 to30 carbon atoms, including their isomers, may be effective as softeningagents. Furthermore, for example, alkyl carboxylic acids, alkenylcarboxylic acids, polyalkenyl carboxylic acids, aryl carboxylic acids,mono-, di-, and tri-carboxylic acids, each of which containing from 1 to30 carbon atoms, including their isomers, may be effective as softeningagents. Carboxylic acids are particularly effective as softening agents.Less than 0.1 wt % carboxylic acid can noticeably reduce the stiffnessof a VSR.

Boron-bridge-opening-chemicals are most effective at facilitating theopening and closing of boron bridges in VSR compositions of theinvention when those chemicals remain in the silicone phase—that is,when they do not phase-separate because of chemical incompatibility orundergo a phase-change to solid or gas. In other words, a preferredboron-bridge-opening-chemical is one that (1) is miscible in VSRcompositions of the invention, (2) has a low melting temperature, and(3) has a low vapor pressure. See, e.g., Examples 1-13, and 60.

Many primary alcohols and carboxylic acids (i.e., hydrocarbons having asingle hydroxyl or carboxyl group) are miscible in silicones and thussatisfy (1). Also, many or most silicones having one or more silanol(Si—OH), carbinol (C—OH), and/or carboxyl groups satisfy (1). Examplesinclude primary alcohols such as, for example, 2-propanol, hexanol,decanol, 2-ethylhexanol, lauryl alcohol, stearyl alcohol, oleyl alcohol,and isostearyl alcohol, carboxylic acids such as, for example, aceticacid, 2-ethylhexanoic acid, lauric acid, stearic acid, oleic acid, andisostearic acid, and silicones such as, for example, silanol-terminatedpolydimethylsiloxanes. See, e.g., Examples 1-13, and 60.

Satisfying (2) and (3) simultaneously requires more careful selection ofchemicals. That is because lower-molecular-weight alcohols andcarboxylic acids are often liquid at the relevant temperatures, but havesubstantial vapor pressures, whereas higher-molecular-weight alcoholsand carboxylic acids are often solid at the relevant temperatures.Fortunately, higher-molecular-weight alcohols and carboxylic acids thathave branched chains and/or carbon-carbon double bonds tend to be liquidat relevant temperatures yet have low vapor pressures. Examples includeprimary alcohols such as, for example, 2-ethylhexanol, oleyl alcohol,linoleyl alcohol, 2-hexyldecanol, and isostearyl alcohol, and carboxylicacids such as, for example, 2-ethylhexanoic acid, oleic acid, linoleicacid, 2-hexyldecanoic acid, and isostearic acid. See, e.g., Examples1-13, and 60.

Double bonds are chemically fragile and can be damaged by light andchemicals. In one embodiment, the boron-bridge-opening-chemicals have nocarbon-carbon double bonds and thus high chemical stability. They arehigher-molecular-weight, fully saturated fatty alcohols and carboxylicacids that are branched or that are branched with multiple branch-pointsso that they remain liquid even at the lowest temperatures to which thematerials of this invention will be subjected and yet have low vaporpressures. Examples include primary alcohols such as, for example,2-ethylhexanol, 2-hexyldecanol, and isostearyl alcohol, and carboxylicacids such as, for example, 2-ethylhexanoic acid, 2-hexyldecanoic acid,and isostearic acid. See, e.g., Examples 1-13, and 60.

Examples of isostearyl alcohol and isostearic acid are available assynthetic products of Nissan Chemical America Corporation. They remainliquid down to extremely low temperatures yet have very low vaporpressures. They are odorless, safe, and miscible with silicones. Theydiffuse easily into cured VSR compositions of the invention and do notexude from those VSR of the invention. The four commercial compoundsare:

Iso-Stearyl Alcohol FO-180 Melting Point: <−90° C. Boiling Point: 295°C.

Iso-Stearyl Alcohol FO-180N Melting Point: <−30° C. Boiling Point: 306°C.

Iso-Stearic Acid Melting Point: <−70° C. Boiling Point: 311° C.

Iso-Stearic Acid N Melting Point: <−30° C. Boiling Point: 320° C.

Another preferred softening agent that may be included is unsaturatedoleic acid, despite containing a double bond, which reduces its chemicalstability. See, e.g., Examples 1, 2, and 74-77.

Arizona Chemicals also produces an isostearic acid blend as theirproduct “Century 1105.” Century 1105 is less preferred as aboron-bridge-opening-chemical because it tends to exude from finishedVSR compositions of the invention and freezes at 4° C. Nonetheless, thisArizona saturated fatty acid is likely more chemically stable than theunsaturated oleic acid. See, e.g., Example 49.

While water is not very miscible in VSR compositions of the inventionand has a high vapor pressure, its abundance in the atmosphere and insome of the environments to which VSR compositions of the invention areexposed can maintain its concentration in VSR compositions of theinvention so that it acts as an important boron-bridge-opening-chemical.See, e.g., Example 48. Water may also hydrolyze esters that may haveformed in the VSR of the invention and thus reduce the availability ofother softening agents. By releasing those softening agents from theirester form, water increases their effectiveness at softening the VSR.

Volatile boron-bridge-opening-chemicals are useful during thepreparation and molding of VSR compositions of the invention and totemporarily reduce the viscosities of borosilicones. By increasing therates of opening and closing of the boron-based temporary crosslinks,these chemicals allow uncured VSR compositions of the invention to flowmore easily through processing and molding equipment. Once the volatilechemicals have evaporated, they no longer have any effect on the VSRcompositions of the invention. Similarly, these chemicals reduce theviscosities of borosilicones only until they evaporate, after which theyhave no effect on the borosilicones. See, e.g., Example 46 and 53-60.For example, acetic acid is particularly effective as a temporarysoftening agent that makes compounding, processing, and molding theconstituents of a VSR much easier. See, e.g., Examples 29-32, 41-44, 46,48, 53-60, and 62. This temporary softening disappears once the aceticacid has evaporated or otherwise left the finished VSR.

The softening agents may be present in any amount sufficient to make theaverage lifetime of the temporary crosslink of shorter duration than theaverage lifetime of the temporary crosslink in the absence of thesoftening agent. For example, the softening agent may be present in theVSR compositions of the invention in an amount ranging from about 0.01wt % to 5.0 wt %, such as, for example, from about 0.02 wt % to about4.0 wt %, such as, for example, from about 0.03 wt % to about 3.0 wt %,based on the total weight of the VSR composition. Preferably, thesoftening agent may be present in the VSR compositions of the inventionin an amount ranging from about 0.05 wt % to about 2.0 wt %, based onthe total weight of the VSR composition. In other cases, the softeningagents may be present in even lower amounts. For example, whenatmospheric water from the environment is used as the softening agent,less than about 0.01 wt % may be present and still have a softeningeffect. Acetic acid may be present in amount less than about 0.01 wt %and still have a softening effect. Heavy acids, such as oleic acid andisostearic acid, may be present in an amount as high as about 2.0 wt %,but more preferably, about 1.2 wt %, and even more preferably, about 0.8wt % or less, may be used to render a softening effect.

Catalysts, Moderators, Accelerators, Additives, and Fillers

In addition to the softening agents mentioned above, the VSRcompositions of the invention may alsoinclude any catalysts, moderators,accelerators, additives, and fillers known for use with silicone rubbercompositions such as those discussed above. Catalysts that may be usedin condensation-cure silicones include, but, are not limited to, tin andtitanium catalysts (e.g., dibutyldilauryltin, bis(2-ethylhexanoate)tin,titanium dibutoxide(bis-2,4-pentanedionate), and titaniumdiisopropoxide(bis-2,4-pentanedionate)), and associated accelerators(e.g., AeroMarine Accelerator). Catalysts that may be used inaddition-cure silicones include, but, are not limited to, platinum andrhodium catalysts (e.g., chloroplatinic acid, Karstedt catalyst(platinum-divinyltetramethyldisiloxane complex), Ossko catalyst(platinum carbonyl cyclovinylmethylsiloxane complex), Lamoreaux catalyst(platinum-octanaldehyde/octanol complex), andtris(dibutylsulfide)rhodium trichloride)), and associated moderators(e.g., 1,3-divinyltetramethyldisiloxane,1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane).

A condensation-cure catalyst may be present in the VSR compositions ofthe invention in an amount ranging from about 0.001 wt % to about 10.0wt %, such as, for example, from about 0.005 wt % to about 8.0 wt %,such as, for example, from about 0.01 wt % to about 6.0 wt %, based onthe total weight of the VSR composition. Preferably, a condensation-curecatalyst may be present in the VSR compositions of the invention in anamount ranging from about 0.05 wt % to about 4.0 wt %, based on thetotal weight of the VSR composition. An addition-cure catalyst may bepresent in the VSR compositions of the invention in an amount, based onthe catalyst's precious metal content alone, ranging from about 0.5 ppmto about 500 ppm, such as, for example, from about 1 ppm to about 100ppm, such as, for example, from about 2 ppm to about 50 ppm. Preferably,an addition-cure catalyst may be present in the VSR compositions of theinvention in an amount, based on the catalyst's precious metal contentalone, ranging from a bout 3 ppm to about 30 ppm. The peroxidecrosslinking agent used in peroxide-cure silicones is normally activatedby heat rather than a catalyst, but it is also possible to include acatalyst to assist the reactions. The accelerators may be present in theVSR compositions of the invention in an amount ranging from about 0.01wt % to 6.0 wt %, such as, for example, from about 0.02 wt % to about5.0 wt %, such as, for example, from about 0.04 wt % to about 4.0 wt %,based on the total weight of the VSR composition. Preferably, theaccelerator may be present in the VSR compositions of the invention inan amount ranging from about 0.1 wt % to about 3.3 wt %, based on thetotal weight of the VSR composition. The moderators, which are optional,may be present in the VSR compositions of the invention in an amountranging from about 0.001 wt % to 1.0 wt %, such as, for example, fromabout 0.005 wt % to about 0.5 wt %, such as, for example, from about0.01 wt % to about 0.2 wt %, based on the total weight of the VSRcomposition. Preferably, the moderator may be present in the VSRcompositions of the invention in an amount ranging from about 0.02 wt %to about 0.1 wt %, based on the total weight of the VSR composition.

Peroxides, such as, for example, DCP and VX, may be present in the VSRcompositions of the invention in an amount ranging from about 0.05 wt %to about 5.0 wt %, such as, for example, from about 0.1 wt % to about4.0 wt %, such as, for example, from about 0.2 wt % to about 3.0 wt %,based on the total weight of the VSR composition. Preferably, a peroxidemay be present in the VSR compositions of the invention in an amountranging from about 0.4 wt % to about 2.0 wt %, based on the total weightof the VSR composition. One of skill in the art would understand thatperoxides may be considered either crosslinking agents or as agents thatinitiate crosslinking.

Fillers may be used in an amount up to about 80 wt % of rubbercomposition. For example, the filler may be present in the VSRcompositions of the invention in an amount ranging from about 1.0 wt %to 80.0 wt %, such as, for example, from about 2.0 wt % to about 50.0 wt%, such as, for example, from about 5.0 wt % to about 40.0 wt %, basedon the total weight of the VSR composition. Preferably, the filler maybe present in the VSR compositions of the invention in an amount rangingfrom about 8.0 wt % to about 30.0 wt %, based on the total weight of theVSR composition. As is known in the art the amount of filler used willdepend on the particular filler and the desired end use of the VSRcomposition. For example, a VSR composition of the invention may containa reinforcing filler such as fumed silica or clay particles.Hexamethylenedisilazane treated fumed silicas from Gelest, Inc., andfrom Cabot Corp. are preferred reinforcing fillers as are the Garamiteclays from Southern Clay Products. Reinforcing fillers may also include,for example, fumed alumina, fumed titania, calcium metasilicate, andsilicon dioxide. Density-reducing fillers such as microballoons ormicrospheres, e.g., Expancel microspheres from AkzoNobel may also beused. The amount of density-reducing fillers depends upon the desireddensity of the final product. Other traditional fillers such aspigments, insulators, and other inorganic fillers may be used as knownin the art.

Adding one or more mixed mineral thixotropes (MMTs), such as, forexample, Garamite 1958 or Garamite 2578 (Southern Clay Products), as anadditive to VSR compositions of the invention greatly increases theviscosity of uncured VSR compositions of the invention and renders thatfluid thixotropic. MMTs also increase the tensile strengths and tearstrengths of VSR compositions of the invention when those MMTs are addedas reinforcing fillers. Dispersing additives such as MMTs can be doneeffectively using an ordinary blender or immersion blender. Thedispersed MMTs (e.g., Garamite 1958 or Garamite 2578) acts asreinforcing filler for the VSR compositions of this invention. Forexample, adding 5 wt % or more MMTs, such as Garamite 1958 to STPDMS,may substantially increase the elastic modulus, viscous modulus, tensilestrength, and tear resistance of VSR compositions of the invention. WhenMMTs are added in the amount of 10 weight percent or more, the increasesin tensile strength and tear strength may be very significant. Forexample, adding 12.5 wt % or more Garamite 1958 to STPDMS isparticularly effective at increasing the elastic modulus, viscousmodulus, tensile strength, and tear resistance of a VSR composition ofthe invention made from that STPDMS.

MMTs, such as, for example, Garamite 1958 and Garamite 2578, are mosteffective at increasing the tensile strength and tear strength of VSRcompositions of the invention when the MMT(s) are first blended into thesilicone base and then heat-treated to evaporate a substantial fractionof the water present in the pre-heat-treated blend. The heat-treatmentcan be done at a temperature between 50 and 220° C., but is preferablydone at a temperature between 150 and 200° C. Heat-treatment isparticularly effective when the MMT-silicone blend is heated as a thinlayer for between 1 and 20 minutes, so that the water is able toevaporate easily and thoroughly from the mixture. VSR compositions ofthe invention made from MMT-silicone blends that have, been heat-treatedas thin layers at between 150 and 200° C. for between 1 and 20 minuteshave particularly large tensile strengths and tear resistances. See,e.g., Example 2.

When a blend consisting of MMTs dispersed in STPDMS is heated as a thinlayer to temperatures ranging from 50° C. to 220° C., moisture isvisibly driven out of the blend and the blend's viscosity and thixotropyboth increase substantially. This heat treatment is particularlyeffective when care is taken not to evaporate or sublime a significantfraction of the quaternary ammonium compound(s) contained in the MMTs.Blending from 1.2.5 wt % to 20 wt % Garamite 1958 in 90-120 cSt STPDMSand then heat-treating that blend at 150° C. to 200° C. produces anexceptionally viscous and thixotropic fluid.

Heat-treated blends of MMTs in STPDMS produce VSR compositions of theinvention with excellent characteristics and that heat treatment of adispersion of MMT in STPDMS can increase the elastic modulus, viscousmodulus, tensile strength, and tear resistance of the resultingviscoelastic rubber. Heat-treated blends of 12.5 wt % to 20 wt %Garamite 1958 in 90-120 ca STPDMS produce VSR compositions of theinvention with exceptionally large elastic moduluses, viscous moduluses,tensile strengths, and tear resistances. Even when heat-treated blendsof MMTs in STPDMS incorporating other materials, such as plasticmicrospheres, they can still form VSR compositions of the invention withincreased elastic moduluses, viscous moduluses, tensile strengths, andtear resistances.

Vulcanizable borosilicones of the invention can produce foamed VSRcompositions of the invention when blowing agents, such as, for example,AkzoNobel Expancels, sodium bicarbonate, acodicarbonamide, Exocerol®,Hydrocerol®, Nitrosan®, dinitropenfamethylenetetramine,p-tolylsulfonylhydrazide, 4,4-oxybis(benzylsulfonylhydrazide),5-phenyhetrazol, and p-tolylsulfonylsemicarbazide, are incorporated intothem prior to vulcanization. Those blowing agents can be expanded priorto or during the vulcanization process. A blowing agent may be presentin the VSR compositions of the invention in an amount ranging from about0.01 wt % to 10.0 wt %, such as, for example, from about 0.02 wt % toabout 5.0 wt %, such as, for example, from about 0.04 wt % to about 4.0wt %, based on the total weight of the VSR composition. Preferably, ablowing agent may be present in the VSR compositions of the invention inan amount ranging from about 0.1 wt % to about 3.0 wt %, based on thetotal weight of the VSR composition.

In one embodiment, vulcanizable borbsilicones of the invention canproduce foamed VSR compositions of the invention when compoundscontaining hydroxyl group(s) (e.g., water, alcohols, carboxylic acids,silanols) are incorporated into them prior to addition-curevulcanization. Those hydroxyl groups react with hydrosiloxanes torelease hydrogen gas, which foams the VSR, or esterify to release water,which may then foam the VSR.

In another embodiment, vulcanizable borosilicones of the invention canproduce foamed VSR compositions of the invention when a gas (e.g.,nitrogen) is dissolved into the borosilicone at high pressure and thatpressure is abruptly released just prior to vulcanization. The dissolvedgas comes out of solution and foams the VSR.

Furthermore, microencapsulated permanent crosslinking agents, peroxides,and/or catalysts can be embedded in the viscoelastic silicone rubbers ofthis invention to render them self-healing. When the silicone rubber ofthe invention is torn by impact or excessive strain, themicroencapsulated permanent crosslinking agent and/or catalyst isreleased locally. That agent and/or catalyst then forms new permanentcrosslinks that bridge the tear and reestablished the network ofpermanent crosslinks. This self-healing process takes advantage of thereactive sites that appear whenever temporary crosslinks open. Permanentcrosslinks will replace temporary crosslinks in the vicinity of thetear, healing the tear. It also takes advantage of the fact that thetemporary crosslinks will hold the two sides of the tear together duringthe permanent crosslinking process.

Passivating Agents

The surface of a VSR of the invention can be passivated (i.e., renderednonself-sticky) in one of several ways: (1) by exposing that surface totitanium compounds, such as, for example, titanium (IV) isopropoxide(see, e.g., Example 47), (2) by exposing that surface tocondensation-cure catalysts such as, for example, AeroMarine SiliconeAccelerator, with or without additional condensation-cure crosslinkingagents, and/or (3) by coating that surface with condensation-curesilicone rubber formulations such as, for example, Wacker A07 or DowCorning 734. Silicone-organic surfactants that tend to phase separatefrom silicones can be used to coat and passivate the surfaces of VSRcompositions of the invention as well. See, e.g., Example 61.

Methods of Preparation

The VSR compositions may be prepared using the same techniques known toprepare other silicone rubber compositions. For example, VSRcompositions of the invention can be made using any of the knownsilicone crosslinking and curing chemistries, including condensationcure, addition cure, and peroxide cure silicone chemistries, as well asall other known organo-silicone chemistries, including cures based onisocyanates and epoxies. See, e.g., Examples 26-28 and 33-35. Catalystsand/or peroxides known in the art may be used and in similar amounts aswith other silicone rubber compositions. Various methods of preparingthe VSR compositions are described in the examples below.

VSR compositions of the invention that form permanent crosslinks usingthe condensation cure can proceed without catalysts. For example,acetoxy groups bound to silicon atoms can react with silanol groups inthe absence of catalysts. See, e.g., Examples 26-28 and 33-35.

In one method to prepare a VSR composition of the invention, thepolyorganosiloxane base may first be reacted with a temporarycrosslinking agent, such as, for example, a boron-containingcrosslinking agent, under conditions to produce a borosilicone compound.This establishes the temporary crosslinking network within thecomposition. The reaction between the silanol groups and theboron-containing crosslinking compound is rapid, such that when thesilanol-terminated polyorganosiloxane base is combined with bothcrosslinking agents the temporary crosslinking network will form beforethe permanent crosslinking network. To establish the permanentcrosslinking network a siloxane and/or carbon bond-forming crosslinkingagent and an optional catalyst are added to the borosilicone compound toform a mixture. That mixture may optionally include a filler and/or asolvent for one or more components. In some instances the borosiliconecompound is itself still a liquid (its gel point is not reached) and theother reactants can be directly added to the liquid borosiliconecompound. The mixture is then cured under conditions sufficient to forma VSR composition. The curing step typically takes place in a mold sothat the mixture is placed in a mold and then cured to establish itspermanent equilibrium state. The VSR compounds of the invention may bemolded into any desired shape. Alternatively, and with the variousembodiments mentioned, a VSR composition of the invention may also beprepared by: combining a silanol-terminated polyorganosiloxane base witha siloxane and/or carbon bond-forming crosslinking agent, a catalyst, anoptional filler, and an optional foaming agent to form a mixture; addinga boron-containing crosslinking agent to the mixture; and curing themixture under conditions sufficient to form a VSR composition.

In another embodiment, two-part RTV and HTV viscoelastic siliconerubbers can be formulated by separating the chemicals necessary to formviscoelastic silicone rubbers into two stable groupings—groupings thatdo not cure independently and therefore remain fluid for long periods oftime. To form the viscoelastic silicone rubbers, those two groups arecombined so that the curing reaction can commence, either at roomtemperature for RTV formulations or at elevated temperature for HTVformulations.

Foamed rubber compositions using the VSR compositions of the inventionmay also be prepared using techniques known in the art. For example afoaming agent may be added to the mixture prior to placing it in a moldor at least prior to curing the mixture. Alternatively, a pressurizedgas such as nitrogen may be injected into the mixture during the curingstep. Foamed rubber compositions may also be achieved by gas evolutionas a by-product of the curing process. Each of these methods, which areknown in the art, is described in the examples below.

Uses and Applications of Viscoelastic Siloxane Rubber Compositions

The VSR compositions of the invention may be used in the same way andapplications as other viscoelastic rubber compositions such as bouncingputty, viscoelastic urethane foams, and other known viscoelasticcompositions and high-resilience compositions. Common among theapplications and uses of bouncing putty and other such compositions aretime delays, motion rate governors, shock absorbing devices, motioncoupling devices, furniture leveling devices, adaptive padding, andtherapy putties. For a number of these uses, however, the bouncing puttyrequires containment to keep the putty from flowing beyond its intendedregion—something that the VSR compositions of the invention do notrequire. More specific uses and applications include, but are notlimited to, acoustic coupling devices; arch supports for shoes; bodyarmor; cargo restrains; cleaning rollers and pads; doorstops; earplugs;exercise devices; furniture leveling devices; grips for tree shakers;grips for writing implements; heel stabilizers for shoes; impact forcedispersion devices and equipment; insoles for shoe; mattresses; momentumdispersion devices and equipment; motion and intrusion sensors; motionrate governors; orthotics, pads, separators, and other non-rigidstructures for human health and comfort; padding and support forflooring materials; padding for bicycle seats; padding for boots;padding for cameras; padding for crutches; padding for earpieces;padding for firearms; padding for hearing aids; padding for shoulderstraps; padding for sports equipment; prostheses; physical therapymaterials; safety cushions and pads; seals for sound, heat, andchemicals; shock dispersion devices and equipment; straps and cords;time delay devices; toys; vibration, rattling, chattering, buzzing, andmotion snubbers; vibration transducers; and wedges and other retainingdevices.

The VSR compounds of the invention have a tacky surface. This allows therubber composition to adhere to another material such as cloth. Thetacky surface of the compounds may also be passivated by coating thesurface with a solution containing a further amount of a siloxanebond-forming crosslinking agent, such as TEOS, and a catalyst. Thesolution may also contain additional silanol-terminatedpolyorganosiloxanes. Passivating the surface layer removes itstackiness.

EXAMPLES

The materials used in the examples below are listed in Table 3. In theexamples below an expression such as “XXX at nn % saturation” or “nn %XXX,” where XXX is a compound that can react with silanol groups, refersto the amount of XXX added to a particular silicone blend that issufficient to bind with nn % of the silanol groups in that siliconeblend. Similarly, the expression “YYY at nn wt %” or “nn wt % YYY,”where YYY is a compound or material that can be added to a siliconeblend, refers to the amount of YYY added to a particular silicone blendthat is nn % of the initial weight of that silicone blend. ShoreHardness was measured according to ASTM 2240.

TABLE 3 PDMS trimethyl-terminated polydimethylsiloxane fluid STPOSsilanol-terminated polyorganosiloxanes STPDMS silanol-terminatedpolydimethylsiloxane fluid 16-32 cSt STPDMS STPDMS having a viscosity of16-32 cSt (Gelest DMS-S12) 45-85 cSt STPDMS STPDMS having a viscosity of45-85 cSt (Gelest DMS-S15) 90-120 cSt STPDMS STPDMS having a viscosityof 90-120 cSt (Gelest DMS-S21) 700-800 cSt STPDMS STPDMS having aviscosity of 700-800 cSt (Gelest DMS-S27) 3500 cSt STPDMS STPDMS havinga viscosity of 3500 cSt (Gelest DMS-S33) BA boric acid, B(OH)₃ TMBtrimethyl borate, B(OCH₃)₃ TIP titanium(IV) isopropoxide (Alfa/Aesar)PDEOS polydiethoxysilane (Gelest PSI-021) TEOS tetraethoxysilane (GelestSIT7110.0) MTEOS methyltriethoxysilane (Alfa/Aesar) VTASvinyltriacetoxysilane (Gelest SIV9098.0) VTEOS Vinyltriethoxysilane(Alfa/Aesar) IP Isopropanol TFS hexamethyldisilazane-treated fume silica(Gelest SIS6962.0 of Cab-o-Sil TS- 530) TO tin II octoate (GelestSNB1100) AMA AeroMarine Rapid Set Silicone Cure Accelerator (AeroMarineProducts, San Diego, CA). PMHS polymethylhydrosiloxane (Gelest HMS-991)PMHS-PDMS Polymethylhydrosiloxane-PDMS copolymer (Gelest HMS-301)copolymer DCP dicumyl peroxide (Gelest SID3379.0) VX2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (Luperox ® 101) G1958Garamite 1958 (Southern Clay Products) ISAlc Iso-Stearic Alcohol, ahighly branched isomer of stearyl alcohol (Nissan Chemical FO-180) ISAIso-Stearic Acid, a highly branched isomer of stearic acid (NissanChemical Iso-Stearic Acid) ISAN Iso-Stearic Acid-N, a branched isomer ofstearic acid (Nissan Chemical Iso- Stearic Acid) Pt 3-3.5%Platinum-divinyltetramethyldisiloxane complex, Karstedt catalyst (GelestSIP6830.3) TVTMTS1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane moderator(Gelest SID4613.0) Struksilon 8018 silicone-polyether surfactant(Schill + Seilacher Struksilon 8018)

Example 1 Oleic-Acid-Softened Condensation-Cure VSR Based on 40% TEOSand 65% TMB in 30 wt % TFS Reinforced 90-120 cSt STPDMS

30 wt % TFS was dispersed in 90-120 cSt STPDMS using a 3-roll mill. To40.0 g of this blend, 0.330 g TMB (65% saturation), 0.667 g AMA (2 wt%), and 0.331 g TEOS (40% saturation) were added. The mixture wasdegassed in vacuum, placed in a sheet mold that measured 3″×3″×0.1875″,and allowed to cure and dry for a week at 63° C. in a dehydrator.

The cured sample was immersed in oleic acid for several days. Whenremoved and blotted dry, the sample sheet was highly viscoelastic andvery soft. It deformed easily when touched or squeezed, but recoveredcompletely over a period of seconds. Its Shore Hardness was determinedto be 65O at t=0, 20O at t=5 sec, and 12O at t=60 sec.

Example 2 Oleic-Acid-Softened Condensation-Cure VSR Based on 50% TEOSand 60% TMB in 12.5 wt % G1958-Reinforced 90-120 cSt STPDMS

12.5 wt % G1958 was dispersed in 90-120 cSt STPDMS using an immersionblender. This blend was then heat-treated as a thin layer on an aluminumsurface for 5 minutes at 180° C. The resulting blend was extremelyviscous and thixotropic.

To 40.0 g of this blend, 0.352 g TMB (60% saturation), 0.711 g AMA (2 wt%), and 0.441 g TEOS (50% saturation) were added. The mixture wasdegassed in vacuum, placed in a sheet mold that measured 3″×3″×0.1875″,and allowed to cure and dry for a week at 63° C. in a dehydrator.

The fully cured sample was immersed in oleic acid for several days. Whenremoved and blotted dry, the sample sheet was highly viscoelastic andvery soft. It deformed easily when touched or squeezed, but recoveredalmost completely over a period of seconds. Its Shore Hardness wasdetermined to be 35A, 54O at t=0, 3A, 19O at t=5 sec, and 0A, 9O at t=60sec.

Example 3 ISAIc-Softened Condensation-Cure VSR Based on 60% MTEOS and50% TMB in 15 wt % TFS-Reinforced 90-120 cSt STPDMS

15 wt % TFS was dispersed in 90-120 cSt STPDMS using a 3-roll mill. To40.0 g of this blend, 0.800 g ISAIc (2 wt %), 0.289 g TMB (50%saturation), 0.700 g AMA (2 wt %), and 0.594 g MTEOS (60% saturation)were added. The mixture was degassed in vacuum, placed in a sheet moldmeasuring 3″×3″×0.1875″, and allowed to cure for 24 hours at 40° C. in adehydrator.

The resulting sheet was highly viscoelastic and medium soft. Its ShoreHardness was determined to be 22A, 35O at t=0, 12A, 26O at t=5 sec, and7A, 21O at t=60 sec. It deformed fairly easily when touched or squeezed,but recovered completely over a period of seconds. A steel ball droppedon its surface rebounded almost to its original height.

Example 4 ISAN-Softened Condensation-Cure VSR Based on 60% MTEOS and 50%TMB in 15 wt % TFS-Reinforced 90-120 cSt STPDMS

15 wt % TFS was dispersed in 90-120 cSt STPDMS, using a 3-roll mill. To40.0 g of this blend, 0.400 g ISAN (1 wt %), 0.289 g TMB (50%saturation), 0.350 g AMA (1 wt %), and 0.594 g MTEOS (60% saturation)were added. The mixture was degassed, placed in a sheet mold measuring3″×3″×0.1875″, and allowed to cure for 24 hours at 40° C. in adehydrator.

The resulting sheet was highly viscoelastic and very soft. Its ShoreHardness was determined to be 38A, 55O at t=0, 20A, 36O at t=5 sec, and13A, 29O at t=60 sec. It deformed easily when touched or squeezed, butrecovered completely over a period of seconds. A steel ball dropped onits surface rebounded almost to its original height.

Example 5 ISAN-Softened Condensation-Cure VSR Based on 70% MTEOS and 40%TMB in 20 wt % TFS-Reinforced 700-800 cSt STPDMS

20 wt % TFS was dispersed in 700-800 cSt STPDMS using a 3-roll mill. To40.0 g of this blend, 0.400 g ISAN (1 wt %), 0.051 g TMB (40%saturation), 0.350 g AMA (1 wt %), and 0.154 g MTEOS (70% saturation)were added. The mixture was degassed in vacuum, placed in a sheet moldmeasuring 3″×3″×0.1875″, and allowed to cure for 24 hours at 40° C. in adehydrator.

The resulting sheet was highly viscoelastic and extremely soft. ItsShore Hardness was determined to be 22A, 38O at t=0, 12A, 26O at t=5sec, and 7A, 20O at t=60 sec. It deformed easily when touched orsqueezed, but recovered completely over a period of seconds. A steelball dropped on its surface rebounded to a fraction of its originalheight.

Example 6 ISAN-Softened Condensation-Cure VSR Based on 70% MTEOS and 40%TMB in 20 wt % TFS-Reinforced 3500 cSt STPDMS

20 wt % TFS was dispersed in 3500 cSt STPDMS using a 3-roll mill. To40.0 g of this blend, 0.400 g ISAN (1 wt %), 0.021 g TMB (40%saturation), 0.350 g AMA (1 wt %), and 0.064 g MTEOS (70% saturation)were added. The mixture was degassed in vacuum, placed in a sheet moldmeasuring 3″×3″×0.1875″, and allowed to cure for 24 hours at 40° C. in adehydrator.

The resulting sheet was highly viscoelastic and extremely soft. ItsShore Hardness was determined to be 20O at t=0, 11O at t=5 sec, and 4Oat t=60 sec. It deformed easily when touched or squeezed, but recoveredcompletely over a period of seconds. A steel ball dropped on its surfacerebounded to a small fraction of its original height.

Example 7 Peroxide-Cure VSR Based on 50% HTV Silicone and 50%(ISAN-Softened 16-32 cSt STPDMS-Based Borosilicone), Blended andCrosslinked Using VX

ISAN-softened 16-32 cSt STPDMS-based 100%-saturated borosilicone(Borosilicone A) was made by adding 12.788 g TMB (100% saturation) and0.254 g ISAN (0.25 wt %) to 101.441 g 16-32 cSt STPDMS. The mixture washeated to 150° C. for 3 hours in a convection oven to evaporate theresulting methanol and further dried as a thin sheet at 63° C. in adehydrator overnight.

16.0 g of the softened borosilicone was combined with 16.0 g of WackerR401/50 HTV silicone and kneaded together until the mixture washomogeneous. 0.080 g of VX crosslinker was added and the mixture waskneaded again until homogeneous. The viscous blend was squeezed into aTeflon sheet mold, 3″×3″×0.1875″ deep. The mold was capped with a Teflonsheet and was placed in an aluminum press. The aluminum press was boltedclosed with the help of a 20 ton hydraulic press. The press and moldassembly were heated to 165° C. for 30 minutes. After cooling the moldto room temperature, the finished VSR sample was removed.

This VSR had a Shore Hardness of 52A, 60O at t=0, 11A, 31O at t=5 sec,and 4A, 12O at t=60 sec. It could be stretched slowly to more than 4times its original width and returned gradually to its original shape.

Example 8 Peroxide-Cure VSR Based on 60% HTV Silicone and 40% (ISANSoftened 16-32 cSt STPDMS-Based Borosilicone), Blended and CrosslinkedUsing VX

12.8 g of Borosilicone A was combined with 19.2 g of Wacker R401/50 HTVsilicone and kneaded together until the mixture was homogeneous. 0.096 gof VX crosslinker was added and the mixture was kneaded again untilhomogeneous. The viscous blend was squeezed into a Teflon sheet mold,3″×3″×0.1875″ deep. The mold was capped with a Teflon sheet and placedin an aluminum press, which was bolted closed with the help of a 20 tonhydraulic press. The press and mold assembly were heated to 165° C. for30 minutes. After cooling the mold to room temperature, the finished VSRsample was removed.

This VSR had a Shore Hardness of 60A, 70O at t=0, 17A, 42O at t=5 sec,and 6A, 26O at t=60 sec. It could be stretched slowly to more than 4times its original width and returned gradually to its original shape.

Example 9 Peroxide-Cure VSR Based on 50% HTV Silicone and 50%(Highly-ISAN-Softened 16-32 cSt STPDMS-Based Borosilicone), Blended andCrosslinked Using VX

16.0 g of Borosilicone A was combined with an additional 0.280 g ofISAN, and then with 16.0 g of Wacker R401/50 HTV silicone. The mixturewas kneaded together until it was homogeneous. 0.080 g of VX crosslinkerwas added and the mixture was kneaded again until homogeneous. Theviscous blend was squeezed into a Teflon sheet mold, 3″×3″×0.1875″ deep,and the mold was capped with a Teflon sheet and placed in an aluminumpress, which was bolted closed with the help of a 20 ton hydraulicpress. The press and mold assembly were heated to 165° C. for 30minutes. After cooling the mold to room temperature, the finished VSRsample was removed.

This VSR had a Shore Hardness of 40A, 52O at t=0, 5A, 22O at t=5 sec,and 4A, 11O at t=60 sec. It could be stretched fairly quickly to morethan 4 times its original width and returned gradually to approximatelyits original shape.

Example 10 Peroxide-Cure VSR Based on 50% HTV Silicone and 50%(ISAN-Softened 90-120 cSt STPDMS-Based Borosilicone), Blended andCrosslinked Using VX

ISAN-softened 90-120 cSt STPDMS-based 100%-saturated borosilicone(Borosilicone B) was made by adding 1.723 g TMB (100% saturation) and0.261 g ISAN (0.25 wt %) to 104.4 g 90-120 cSt STPDMS. The mixture washeated to 150° C. for 3 hours in a convection oven to evaporate theresulting methanol and further dried as a thin sheet at 63° C. in adehydrator overnight.

16.0 g of the softened borosilicone was combined with 16.0 g of WackerR401/50 HTV silicone and kneaded together until the mixture washomogeneous. 0.080 g of VX crosslinker was added and the mixture waskneaded again until homogeneous. The viscous blend was squeezed into aTeflon sheet mold, 3″×3″×0.1875″ deep. The mold was capped with a Teflonsheet and placed in an aluminum press, which was bolted closed with thehelp of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed.

This VSR had a Shore Hardness of 44O at t=0, 22O at t=5 sec, and 6O att=60 sec. It could be stretched slowly to more than 4 times its originalwidth and returned gradually to its original shape.

Example 11 Peroxide-Cure VSR Based on 60% HTV Silicone and 40%(ISAN-Softened 90-120 cSt STPDMS-Based Borosilicone), Blended andCrosslinked Using VX

12.8 g of Borosilicone B was combined with 19.2 g of Wacker R401/50 HTVsilicone and kneaded together until the mixture was homogeneous. 0.080 gof VX crosslinker was added and the mixture was kneaded again untilhomogeneous. The viscous blend was squeezed into a Teflon sheet mold,3″×3″×0.1875″ deep. The mold was capped with a Teflon sheet and placedin an aluminum press, which was bolted closed with the help of a 20 tonhydraulic press. The press and mold assembly were heated to 165° C. for30 minutes. After cooling the mold to room temperature, the finished VSRsample was removed.

This VSR had a Shore Hardness of 27A, 45O at t=0, 11A, 31O at t=5 sec,and 4A, 17O at t=60 sec. It could be stretched slowly to more than 4times its original width and returned gradually to its original shape.

Example 12 Addition-Cure VSR Based on 50% HTV Silicone and 50%(ISAN-Softened 90-120 cSt STPDMS-Based Borosilicone), Blended andCrosslinked Using PMHS-PDMS and Pt

A moderated platinum solution (Platinum A) was prepared by dispersing 1wt % Pt and 2 wt % TVTMTS in 10 cSt PDMS.

4.0 g of Borosillcone A was combined with 4.0 g of Wacker R401/50 HTVsilicone and kneaded together until the mixture was homogeneous. 0.080 gof PMHS-PDMS (200% saturation) and 0.160 g of Platinum A were added. Themixture was kneaded again until homogeneous, then squeezed into a1″×1″×0.5″ Delrin mold. An acetate lid was pressed onto the mold. It setovernight and was fully cured after a week. This VSR had a ShoreHardness of 63A, 73O at t=0, 60A, 67O at t=5 sec, and 39A, 57O at t=60sec.

Example 13 Addition-Cure VSR Based on 50% HTV Silicone and 50%(ISAN-Softened 90-120 cSt STPDMS-Based Borosilicone), Blended andCrosslinked Using PMHS-PDMS and Pt

A moderated platinum solution (Platinum B) was prepared by dispersing 1wt % Pt and 3 wt % TVTMTS in toluene.

4.0 g of Borosilicone A was combined with 4.0 g of Wacker R401/50 HTVsilicone and kneaded together until the mixture was homogeneous. 0.025 gof PMHS-PDMS (<100% saturation) and 0.100 g of Platinum B were added.The mixture was kneaded again until homogeneous, and a 20 ton press wasused to squeeze the mixture into a 1.5″ diameter×0.1875″ aluminum moldwith a Teflon gasket. The mixture was then cured at 165° C. for 30minutes. This VSR had a Shore Hardness of 48A, 58O at t=0, 10A, 27O att=5 sec, and 2A, 13O at t=60 sec.

Example 14 Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (90-120cSt STPDMS-Based 200%-Saturated Titanosilicone), Blended and CrosslinkedUsing VX

90-120 cSt STPDMS-based 100%-Saturated titanosilicone was prepared byadding 3.384 g TIP (200% saturation) to 50.0 g 90-120 cSt STPDMS. Themixture was heated to 175° C. for 4 hours in a convection oven toevaporate the volatile reaction products. The mixture was further driedas a thin sheet at 63° C. in a dehydrator overnight.

16.0 g of the titanosilicone was combined with 16.0 g of Wacker R401/50HTV silicone and kneaded together until the mixture was homogeneous.0.080 g of VX crosslinker was added, and the mixture was kneaded againuntil homogeneous. The sticky, viscous blend was squeezed into a Teflonsheet mold, 3″×3″×0.1875″ deep, and the mold was capped with a Teflonsheet and placed it in an aluminum press, which was bolted closed withthe help of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed.

This VSR had a Shore Hardness of 18A, 43O at t=0, 4A, 24O at t=5 sec,and 0A, 10O at t=60 sec. It was stickier than borosilicone-based VSRs.

Example 15 Peroxide-Cure VSR Based on 50% HTV Silicone and 50%(ISAN-Softened 90-120 cSt STPDMS-Based Borotitanosilicone), Blended andCrosslinked Using VX

ISAN softened 90-120 cSt STPDMS-based 100%-Saturated borotitanosiliconewas made by adding 0.550 g TMB (67% saturation), 0.558 g TIP (33%saturation), and 0.125 g ISAN (0.25 wt %) to 50.0 g 90-120 cSt STPDMS.The mixture was heated to 175° C. for 4 hours in a convection oven toevaporate the volatile reaction products and further dried as a thinsheet at 63° C. in a dehydrator overnight.

To 16.0 g of the borotitanosilicone, 0.050 g TMB (25% saturation) wasadded, and the mixture was allowed to dry in the dehydrator at 63° C.for several hours. The mixture was then combined with 16.0 g of WackerR401/50 HTV silicone and kneaded together until the mixture washomogeneous. 0.080 g of VX crosslinker was added and the mixture waskneaded again until homogeneous. The sticky, viscous blend was squeezedinto a Teflon sheet mold, 3″×3″×0.1875″ deep, and the mold was cappedwith a Teflon sheet and placed it in an aluminum press, which was boltedclosed with the help of a 20 ton hydraulic press. The press and moldassembly were heated to 165° C. for 30 minutes. After cooling the moldto room temperature, the finished VSR sample was removed.

This VSR had a Shore Hardness of 14A, 40O at t=0, 3A, 16O at t=5 sec,and 0A, 6O at t=60 sec. It was much stickier than borosilicone-basedVSRs.

Example 16 Peroxide-Cure VSR Based on 50% HTV Silicone and 50%(ISAN-Softened 700-800 cSt STPDMS-Based Borosilicone), Blended andCrosslinked Using VX

ISAN softened 700-800 cSt STPDMS-based 100%-Saturated borosilicone wasmade by adding 0.385 g TMB (100% saturation) and 0.250 g ISAN (0.25 wt%) to 100.0 g 700-800 cSt STPDMS. The mixture was heated to 175° C. for4 hours in a convection oven to evaporate the resulting methanol andfurther dried as a thin sheet at 63° C. in a dehydrator overnight.

16.0 g of the softened borosilicone was combined with 16.0 g of WackerR401/60 HTV silicone and kneaded together until the mixture washomogeneous. 0.080 g of VX crosslinker was added and the mixture waskneaded again until homogeneous. The viscous blend was squeezed into aTeflon sheet mold, 3″×3″×0.1875″ deep. The mold was capped with a Teflonsheet and placed in an aluminum press, which was bolted closed with thehelp of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed. This VSR had a ShoreHardness of 22A, 43O at t=0, 5A, 24O at t=5 sec, and 2A, 13O at t=60sec.

Example 17 Peroxide-Cure VSR Based on a VPCB (50% TMB and 0.25 wt % ISANin 50% VTAS-Crosslinked 90-120 cSt STPDMS), Blended and CrosslinkedUsing VX

A partially crosslinked silicone fluid was made by adding 1.843 g VTAS(50% saturation) and 0.100 g AMA (0.1 wt %) to 100.0 g 90-120 cStSTPDMS. The mixture was stirred vigorous in an open beaker and allowedto cure for 72 hours, at which time the viscosity of the partiallycrosslinked silicone fluid had reached approximately 600 cSt. To thissilicone fluid, 0.250 g ISAN (0.25 wt %) and 0.825 g TMB (50%saturation) were added. The resulting softened VPCB (vulcanizablepartially crosslinked borosilicone) was allowed to dry at roomtemperature as a thin sheet for 48 hours.

To 8.0 g of the VPCB, 0.046 g VX crosslinker was added, and the mixturewas kneaded until homogeneous. The blend was squeezed into a Teflon diskmold, 1.5″ dia×0.1875″ deep, and the mold was capped with a Teflon sheetand placed it in an aluminum press, which was bolted closed with thehelp of a 20 ton hydraulic press. The press and mold, assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed. This unreinforced VSRhad a Shore Hardness of 45O at t=0, 19O at t=5 sec, and 8O at t=60 sec.

Example 18 Peroxide-Cure VSR Based on a VPCB (60% TMB and 0.25 wt % ISANin 50% VTEOS-Crosslinked 90-120 cSt STPDMS), Blended and CrosslinkedUsing VX

A partially crosslinked silicone fluid was made by adding 1.510 g VTEOS(50% saturation) and 0.250 g AMA (0.25 wt %) to 100.0 g 90-120 cStSTPDMS. The mixture was allowed to cure in an open beaker for 6 days, atwhich time the partially crosslinked silicone fluid began to gelslightly. To this silicone fluid, 0.250 g ISAN (0.25 wt %) and 0.990 gTMB (60% saturation) were added. The resulting softened but slightlygelled VPCB was allowed to dry at room temperature as a thin sheet for 1hour.

To 8.0 g of the VPCB, 0.052 g VX crosslinker was added, and the mixturewas kneaded until homogeneous. The blend was squeezed into a Teflon diskmold, 1.5″ dia×0.1875″ deep, and the mold was capped with a Teflon sheetand placed it in an aluminum press, which was bolted closed with thehelp of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed. This unreinforced VSRhad a Shore Hardness of 30O at t=0, 15O at t=5 sec, and 12O at t=60 sec.

Example 19 Peroxide-Cure VSR Based on a VPCB (12.5 wt % G1958Reinforcement and 60% TMB in 50% VTAS-Crosslinked 90-120 cSt STPDMS),Blended and Crosslinked Using VX

A partially crosslinked silicone fluid was made by adding 0.718 g AMA(0.1 wt %) and 13.230 g VTAS (50% saturation) to 717.7 g 90-120 cStSTPDMS. The mixture was stirred vigorous in an open beaker and allowedto cure for 2 hours, at which time the viscosity of the partiallycrosslinked silicone fluid had reached approximately 250 cSt. To 10 g ofthis silicone fluid, 1.250 g G1958 (12.5 wt %) was added and the blendwas heat-treated as a thin layer on a 165° C. surface for 5 minutes.

To 8 g of this heat-treated blend, 0.078 g TMB (50% saturation) wasadded and the resulting VPCB was kneaded until homogeneous andrelatively dry. 0.050 g VX crosslinker was added and the mixture wasagain kneaded until homogeneous. The blend was squeezed into a Teflondisk mold, 1.5″ dia×0.1875″ deep, and the mold was capped with a Teflonsheet and placed it in an aluminum press, which was bolted closed withthe help of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed. This G1958-reinforcedVSR had a Shore Hardness of 55A, 68O at t=0, 36A, 58O at t=5 sec, and17A, 34O at t=60 sec.

Example 20 Peroxide-Cure VSR Based on a VPCB (10 wt % TFS Reinforcementand 60% TMB in 50% VTAS Crosslinked 90-120 cSt STPDMS), Blended andCrosslinked Using VX

A partially crosslinked silicone fluid was made by adding 0.718 g AMA(0.1 wt %) and 13.230 g VTAS (50% saturation) to 717.7 g 90-120 cStSTPDMS. The mixture was stirred vigorous in an open beaker and allowedto cure for 24 hours, at which time the viscosity of the partiallycrosslinked silicone fluid had reached approximately 350 cSt. To 425.1 gof this silicone fluid, 41.3 g Cabot TS-530 TFS (10 wt %) was added anddispersed using a 3-roll mill.

To 416.2 g of this TFS-reinforced partially crosslinked silicone fluid,1.040 g ISAN (0.25 wt %) and 3.748 g TMB (60% saturation) were added andthe resulting VPCB (VPCB A) was kneaded until homogeneous and thenallowed to dry at room temperature as a thin sheet for 24 hours.

To 8.0 g of this VPCB, 0.010 g TMB and 0.040 g VX crosslinker were addedand the mixture was kneaded until homogeneous. The blend was squeezedinto a Teflon disk mold, 1.5″ dia×0.1875″ deep, and the mold was cappedwith a Teflon sheet and placed it in an aluminum press, which was boltedclosed with the help of a 20 ton hydraulic press. The press and moldassembly were heated to 165° C. for 30 minutes. After cooling the moldto room temperature, the finished VSR sample was removed. ThisTFS-reinforced VSR had a Shore Hardness of 40O at t=0, 17O at t=5 sec,and 8O at t=60 sec.

Example 21 Peroxide-Cure VSR Based on 50% HTV Silicone and 50% VPCB (10wt % TFS Reinforcement and 60% TMB in 50% VTAS Crosslinked 90-120 cStSTPDMS), Blended and Crosslinked Using VX

4.0 g of VPCB A and 4.0 g of Wacker R401/60 HTV silicone were combinedand kneaded together until the mixture was homogeneous. To that mixture,0.040 g VX crosslinker was added and the mixture was again kneaded untilhomogeneous. The mixture was squeezed into a Teflon disk mold, 1.5″dia×0.1875″ deep, and the mold was capped with a Teflon sheet and placedit in an aluminum press, which was bolted closed with the help of a 20ton hydraulic press. The press and mold assembly were heated to 165° C.for 30 minutes. After cooling the mold to room temperature, the finishedVSR sample was removed. This VSR had a Shore Hardness of 40A, 60O att=0, 28A, 46O at t=5 sec, and 21A, 37O at t=60 sec.

Example 22 Peroxide-Cure VSR Based on 25% HTV Silicone and 75% VPCB (10wt % TFS Reinforcement and 60% TMB in 50% VTAS Crosslinked 90-120 cStSTPDMS), Blended and Crosslinked Using VX

6.0 g of VPCB A and 2.0 g of Wacker R401/60 HTV silicone were combinedand kneaded together until the mixture was homogeneous. To that mixture,0.040 g VX crosslinker was added and the mixture was again kneaded untilhomogeneous. The mixture was squeezed into a Teflon disk mold, 1.5″dia×0.1875″ deep, and the mold was capped with a Teflon sheet and placedit in an aluminum press, which was bolted closed with the help of a 20ton hydraulic press. The press and mold assembly were heated to 165° C.for 30 minutes. After cooling the mold to room temperature, the finishedVSR sample was removed. This VSR had a Shore Hardness of 38A, 52O att=0, 18A, 32O at t=5 sec, and 11A, 23O at t=60 sec.

Example 23 Peroxide-Cure VSR Based on a VPCB (15 wt % TFS Reinforcementand 60% TMB in 50% VTAS-Crosslinked 90-120 cSt STPDMS), Blended andCrosslinked Using VX

A partially crosslinked silicone fluid was made by adding 0.783 g AMA(0.1 wt %) and 14.432 g VTAS (50% saturation) to 782.9 g 90-120 cStSTPDMS. The mixture was stirred vigorous in an open beaker and allowedto cure for 52 hours, at which time the viscosity of the partiallycrosslinked silicone fluid had reached approximately 1500 cSt. To 774.4g of this silicone fluid, 116.1 g Cabot TS-530 IFS (15 wt %) was addedand dispersed using a 3-roll mill.

To 847.6 g of this TFS-reinforced silicone fluid, 2.119 g ISAN (0.25 wt%) and 7.300 g TMB (60% saturation) were added and the resulting VPCB(VPCB B) was kneaded until homogeneous and then allowed to dry at roomtemperature as a thin sheet for 24 hours.

To 8.0 g of this VPCB, 0.042 g VX crosslinker was added and the mixturewas kneaded until homogeneous. The blend was squeezed into a Teflon diskmold, 1.5″ dia×0.1875″ deep, and the mold was capped with a Teflon sheetand placed it in an aluminum press, which was bolted closed with thehelp of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed. This TFS-reinforcedVSR had a Shore Hardness of 38A, 48O at t=0, 15A, 27O at t=5 sec, and9A, 20O at t=60 sec.

Example 24 Peroxide-Cure VSR Based on a Vulcanizable PartiallyCrosslinked Titanosilicone (60% TIP and 0.25 wt % ISAN in 50%VTEOS-Crosslinked 90-120 cSt STPDMS), Blended and Crosslinked Using VX

A partially crosslinked silicone fluid was made by adding 1.843 g VTAS(50% saturation) and 0.100 g AMA (0.1 wt %) to 100.0 g 90-120 cStSTPDMS. The mixture was stirred vigorously in an open beaker and allowedto cure for 7 days, at which time the viscosity of the partiallycrosslinked, silicone fluid had reached approximately 500 cSt.

To 8.3 g of this silicone fluid, 0.200 g TIP (70% saturation) and 0.020g ISAN (0.25 wt %) were added. The resulting softened vulcanizablepartially crosslinked titanosilicone (VPCT) was kneaded untilhomogeneous and relatively dry.

To 8.0 g of the VPCT, 0.046 g VX crosslinker was added, and the mixturewas kneaded until homogeneous. The blend was squeezed into a Teflon diskmold, 1.5″ dia×0.1875″ deep, and the mold was capped with a Teflon sheetand placed it in an aluminum press, which was bolted closed with thehelp of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed. This unreinforced VSRhad a Shore Hardness of 25O at t=0, 19O at t=5 sec, and 16O at t=60 sec.

Example 25 Peroxide-Cure Foamed VSR Based on 3 wt % Expancels in a VPCB(15 Wt % TFS Reinforcement and 60% TMB in 50% VTAS-Crosslinked 90-120cSt STPDMS), Blended and Crosslinked Using VX

0.120 g Expancels (930 DU 120) and 0.020 g VX crosslinker were added to4.0 g of VPCB B. The mixture was kneaded until homogeneous. The blendwas squeezed into a Teflon disk mold, 1.5″ dia×0.1875″ deep, and themold was capped with a Teflon sheet and placed it in an aluminum press,which was bolted closed. The press and mold assembly were heated to 165°C. for 30 minutes. After cooling the mold to room temperature, thefinished foamed VSR sample was removed. The density of this foamedTFS-reinforced VSR was approximately half that of Example 23 and it hada Shore Hardness of 48O at t=0, 28O at t=5 sec, and 21O at t=60 sec.

Example 26 Addition-Cure VSR Based on a VPCB (100% TMB in 90%VTAS-Crosslinked 700-800 cSt STPDMS), Blended and Crosslinked withPMHSPDMS and Pt

A partially crosslinked silicone fluid was made by adding 0.774 g VTAS(90% saturation) dropwise to 100.0 g 700-800 cSt STPDMS, while stirringvigorously. The mixture was allowed to cure, without catalyst, for 5hours and it became extremely viscous.

To 3.2 g of this partially crosslinked silicone fluid, 0.012 g TMB (100%saturation), 0.030 g of PMHS-PDMS, and 0.005 g of platinum complexsolution (Gelest SIP6830.3) were added. The mixture was kneaded untilhomogeneous. It was formed into a block and allowed to cure overnight atroom temperature. It became a VSR as the result of the addition cure.

Example 27 Peroxide-Cure VSR Based on a VPCB (15 wt % TFS-Reinforcementand 75% TMB in 40% VTAS-Crosslinked 90-120 cSt STPDMS), Blended andCrosslinked Using VX

A partially crosslinked silicone fluid was made by adding 10.009 g VTAS(40% saturation) to 678.7 g 90-120 cSt STPDMS. Prior to this addition,the STPDMS was carefully dried and degassed by stirring it vigorously invacuum for 40 minutes. The fluid bubbled rapidly as moisture and othervolatiles boiled out of it, but after 40 minutes it stopped bubbling.The VTAS was added to the dried STPDMS fluid in a nitrogen-filled glovebox and the mixture was returned to vacuum. It was stirred rapidly undervacuum for 5 minutes, when it again stopped bubbling. The mixture wassealed under an aluminum foil lid and warmed to 60° C. for 18 hours. Itwas then uncovered and allowed to continue curing at room temperaturefor 24 hours. At that time, the fluid's viscosity had increased toapproximately 8,200 cSt, almost 100 times its starting value.

To this partially crosslinked STPDMS, 15 wt % TFS was added anddispersed using a 3-roll mill. To 672.2 g of this reinforced mixture,0.292 g of ISAN (0.05 wt %) and 7.237 g of TMB (75% saturation) wereadded. The resulting VPCB (VPCB C) was stirred until homogeneous andthen spread out to dry at room temperature as a thin layer on apolyethylene plate.

To 8.0 g of this VPCB were added 0.080 g VX (1.0 wt %). The mixture waskneaded to homogeneity, pressed into a Teflon mold with a Teflon lid,and baked at 165° C. for 30 minutes. This TFS-reinforced VSR had a ShoreHardness of 40A, 53 at t=0, 24A, 41O at t=5 sec, and 17A, 26O at t=60sec.

Example 28 Peroxide-Cure VSR Based on a VPCB (15 wt % TFS Reinforcementand 150% TMB in 90% VTAS-Crosslinked 700-800 cSt STPDMS), Blended andCrosslinked Using VX

A partially crosslinked silicone fluid was made by adding 5.239 g VTAS(90% saturation) to 676.7 g 700-800 cSt STPDMS. Prior to this addition,the STPDMS was carefully dried and degassed by stirring it vigorously invacuum for 90 minutes. The fluid bubbled rapidly as moisture and othervolatiles boiled out of it, but after 90 minutes it stopped bubbling.The VTAS was added to the dried STPDMS fluid in a nitrogen-filled glovebox and the mixture was returned to vacuum. It was stirred rapidly undervacuum for 5 minutes, when it again stopped bubbling. The mixture wassealed under an aluminum foil lid and warmed to 60° C. for 18 hours. Itwas then uncovered and allowed to continue curing at room temperaturefor 24 hours. At that time, the fluid's viscosity had increased toapproximately 33,000 cSt, almost 50 times its starting value.

To this partially crosslinked STPDMS, 15 wt % TFS was added anddispersed using a 3-roll mill. To 713.8 g of this reinforced mixture,0.310 g of ISAN (0.05 wt %) and 3.586 g of TMB (150% saturation) wereadded. The resulting VPCB (VPCB D) was stirred until homogeneous, thenspread out to dry at room temperature as a thin layer on a polyethyleneplate.

To 8.0 g of this VPCB were added 0.040 g VX (0.5 wt %). The mixture waskneaded to homogeneity, pressed into a Teflon mold with a Teflon lid,and baked at 165° C. for 30 minutes. This TFS-reinforced VSR had a ShoreHardness of 28A, 46O at t=0; 19A, 35O at t=5 sec, and 13A, 27O at t=60sec.

Example 29 Addition-Cure VSR Based on 50% VPCB (15 wt % TFSReinforcement and 75% TMB in 40% VTAS-Crosslinked 90-120 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% BA in 90-120 cSt STPDMS),Blended and Crosslinked Using PMHS-PDMS and Pt

A moderated platinum solution (Platinum C) was prepared by dispersing 5wt % Pt and 10 wt % TVTMTS in 350 cSt STPDMS.

6.0 g of VPCB C were combined with 3.0 g of HTV silicone (WackerR401/50), 3.0 g borosilicone (100% BA in 90-120 cSt STPDMS), and 0.010 gacetic acid. The resulting 50/25/25 blend was kneaded until homogeneousand then 0.100 g PMHS-PDMS (approximately 100% saturation) and 0.050 gof Platinum C were added. The mixture was kneaded until homogeneous andthen pressed into an aluminum mold with a Teflon lid. It was heated to110° C. for 30 minutes and underwent the addition cure. ThisTFS-reinforced VSR had a Shore Hardness of 27A, 46O at t=0, 11A, 25O att=5 sec, and 1A, 10O at t=60 sec.

Example 30 Addition-Cure VSR Based on 50% VPCB (15 wt % TFSReinforcement and 150% TMB in 90% VTAS-Crosslinked 700-800 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% BA in 90-120 cSt STPDMS),Blended and Crosslinked PMHS-PDMS and Pt

6.0 g of VPCB D were combined with 3.0 g of HTV silicone (WackerR401/50), 3.0 g borosilicone (100% BA in 90-120 cSt STPDMS), and 0.010 gacetic acid. The resulting 50/25/25 blend was kneaded until homogeneousand then 0.100 g PMHS-PDMS (approximately 100% saturation) and 0.050 gof Platinum C were added. The mixture was kneaded until homogeneous andthen pressed into an aluminum mold with a Teflon lid. It was heated to110° C. for 30 minutes and underwent the addition cure. ThisTFS-reinforced VSR had a Shore Hardness of 23A, 40O at t=0, 11A, 26O att=5 sec, and 2A, 11O at t=60 sec.

Example 31 Addition-Cure Foamed VSR Based on 50% VPCB (15 wt % TFSReinforcement and 150% TMB in 90% VTAS-Crosslinked 700-800 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),Blended and Crosslinked Using PMHS-PDMS, Water, and Pt

5.5 g of VPCB D were combined with 2.75 g of HTV silicone (WackerR401/50), 2.75 g borosilicone (100% TMB in 90-120 cSt STPDMS), and 0.010g acetic acid. The resulting 50/25/25 blend was dried as a thin sheet at60° C. for 24 hours, then softened with another 0.015 g acetic acid. Tothis mixture were added 0.020 g BA, 0.018 g of water, 0.345 g ofPMHS-PDMS, and 0.035 g of Platinum C. The overall mixture was kneadeduntil homogeneous.

5.0 g of this mixture was pressed into an aluminum mold having a volumeof 10 cc and covered with a Teflon cap. The mold and mixture were heatedto 110° C. for 30 minutes. The resulting foamed TFS-reinforced VSR had adensity of approximately 0.75 g/cc (it did not completely fill the mold)and a Shore Hardness of 35O at t=0, 26O at t=5 sec, and 12O at t=60 sec.

Example 32 Two-Part Addition-Cure VSR Based on 50% VPCB (15 wt % TFSReinforcement and 150% TMB in 90% VTAS-Crosslinked 700-800 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),Blended Separately with PMHS-PDMS and Pt and Crosslinked when Combined

4.0 g of VPCB D were combined with 2.0 g of HTV silicone (WackerR401/50), 2.0 g borosilicone (100% TMB in 90-120 cSt STPDMS), and 0.004g acetic acid. To a 4.0 g portion of the resulting 50/25/25 blend wereadded 0.075 g PMHS-PDMS, thereby forming Part A. To a second 4.0 gportion of the 50/25/25 blend were added 0.020 g of Platinum C, therebyforming Part B. Each part was kneaded until homogeneous.

After 5 days, Part A and Part B remained unchanged. They were combinedand kneaded together carefully. The combined mixture was pressed into aTeflon mold and heated to 110° C. for 30 minutes. The resultingTFS-reinforced VSR had a Shore Hardness of 43O at t=0, 30O at t=5 sec,and 15O at t=60 sec.

Example 33 Addition-Cure VSR Based on 50% VPCB (15 wt % TFSReinforcement and 150% TMB in 90% VTAS-Crosslinked 700-800 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),Blended, Softened with ISA, and Crosslinked Using PMHS-PDMS and Pt

A partially crosslinked silicone fluid was made by adding 7.312 g VTAS(90% saturation) to 850.0 g 700-800 cSt STPDMS. Prior to this addition,the STPDMS was carefully dried and degassed by stirring it vigorously invacuum for 30 minutes. The fluid bubbled rapidly as moisture and othervolatiles boiled out of it, but after 30 minutes it stopped bubbling.The VTAS was added to the dried STPDMS fluid in a nitrogen-filled glovebox and the mixture was returned to vacuum. It was stirred rapidly undervacuum for 15 minutes, when it again stopped bubbling. The mixture wassealed under an aluminum foil lid and warmed to 60° C. for 18 hours. Itwas then uncovered and allowed to cool to room temperature, where itsviscosity was measured to be approximately 45,000 cSt, approximately 60times its starting value.

To this partially crosslinked STPDMS, 15 wt % TFS was added anddispersed using a 3-roll mill. To 931.6 g of this reinforced mixture,0.466 g of ISAN (0.05 wt %) and 4.681 g of TMB (150% saturation) wereadded. The resulting VPCB (VPCB E) was stirred until homogeneous, andthen spread out to dry for 24 hours at room temperature as a thin layeron a polyethylene plate.

To 100.0 g of this VPCB were added 50.0 g of borosilicone (100% TMB in90-120 cSt STPDMS) and 50.0 g of HTV silicone (Wacker R401/50). Thisresulting 50/25/25 blend (50/25/25 Blend A) was kneaded untilhomogeneous and then dried for 24 hours as a thin sheet at 60° C.

To 8.0 g of this 50/25/25 blend were added 0.008 g ISA (0.1 wt %) andthe softened blend was kneaded until homogenous. Added then were 0.100 gPMHSPDMS, 0.025 g of Platinum C, and several mg of red pigment(Smooth-On Silc-Pig Red). The full combination was kneaded untilhomogeneous, pressed into a Teflon mold, and heated to 110° C. for 30minutes. The resulting red VSR had a Shore Hardness of 42O at t=0, 24Oat t=5 sec, and 15O at t=60 sec.

To a second 8.0 g portion of the 50/25/25 blend were added 0.016 g ISA(0.2 wt %) and the crosslinking procedure was repeated, but with greenpigment (Smooth-On Silc-Pig Green). The resulting green VSR had a ShoreHardness of 37O at t=0, 17O at t=5 sec, and 9O at t=60 sec.

To a third 8.0 g portion of the 50/25/25 blend were added 0.024 g ISA(0.3 wt %) and the crosslinking procedure was repeated, but with red andblue pigment (Smooth-On Silc-Pig Red and Blue). The resulting violet VSRhad a Shore Hardness of 32O at t=0, 13O at t=5 sec, and 5O at t=60 sec.

Example 34 Addition-Cure VSR Based on 50% VPCB (15 wt % TFSReinforcement and 75% TMB in 40% VTAS-Crosslinked 90-120 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),Blended, Softened with ISA, and Crosslinked Using PMHS-PDMS and Pt

To 100.0 g of VPCB C were added 50.0 g of borosilicone (100% TMB in90-120 cSt STPDMS) and 50.0 g of HIV silicone (Wacker R401/50). This50/25/25 blend (50/25/25 Blend B) was kneaded until homogeneous and thendried for 24 hours as a thin sheet at 60° C.

To 8.0 g of this 50/25/25 blend were added 0.008 g ISA (0.1 wt %) andthe softened blend was kneaded until homogenous. Added then were 0.100 gPMHSPDMS, 0.025 g of Platinum C, and several mg of blue pigment(Smooth-On Silc-Pig Blue): The full combination was kneaded untilhomogeneous, pressed into a Teflon mold, and heated to 110° C. for 30minutes. The resulting blue VSR had a Shore Hardness of 44O at t=0, 24Oat t=5 sec, and 15O at t=60 sec.

To a second 8.0 g portion of the 50/25/25 blend were added 0.016 g ISA(0.2 wt %) and the crosslinking procedure was repeated, but with orangepigment (Smooth-On Silc-Pig Fluorescent Orange). The resulting orangeVSR had a Shore Hardness of 38O at t=0, 15O at t=5 sec, and 9O at t=60sec.

The VSRs of Example 34 were observed to be more resilient during impactthan the VSRs of Example 33. Specifically, a dropped 1″ diameter steelball bounced higher from an Example 34 VSR than from an Example 33 VSR,all else being equal.

Example 35 Addition-Cure VSR Based on 50% VPCB (15 wt % TFSReinforcement and 75% TMB in 40% VTAS-Crosslinked 90-120 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),Blended, Softened with ISA, and Crosslinked Using VX

To 8.0 g of 50/25/25 Blend B were added 0.008 g ISA (0.1 wt %) and thesoftened blend was kneaded until homogenous. Added then were 0.060 g VXand several mg of white and red pigments (Smooth-On Silc-Pig White andRed). The full combination was kneaded until homogeneous, pressed into aTeflon mold, and heated to 165° C. for 30 minutes. The resulting pinkVSR had a Shore Hardness of 47O at t=0, 23O at t=5 sec, and 14O at t=60sec.

To a second 8.0 g portion of 50/25/25 Blend B were added 0.016 g ISA(0.2 wt %) and the crosslinking procedure was repeated, but with whiteand blue pigments (Smooth-On Silc-Pig White and Blue). The resulting skyblue VSR had a Shore Hardness of 45O at t=0, 23O at t=5 sec, and 18O att=60 sec.

Example 36 Addition-Cure Foamed VSR Based on 50% VPCB (15 wt % TFSReinforcement and 75% TMB in 40% VTAS-Crosslinked 90-120 cSt STPDMS),25% HTV Silicone, and 25% Borosilicone (100% TMB in 90-120 cSt STPDMS),Blended and Crosslinked Using PMHS-PDMS and Platinum Catalyst and Blownwith High-Pressure Nitrogen

To 8.0 g of 50/25/25 Blend A were added 0.008 g ISA (0.1 wt %) and thesoftened blend was kneaded until homogenous. Added then were 0.100 gPMHS30 PDMS and 0.025 g of Platinum C. The full combination was kneadeduntil homogeneous. 2.0 g of this mixture were formed into a disk andplace in a Teflon-coated high-pressure cell. The cell was filled withnitrogen gas at 1000 psi and this pressure was maintained for 2.5 hours.At the end of that period, the pressure was suddenly released and themixture foamed immediately. The foamed mixture was heated to 110° C. for30 minutes. The resulting foamed VSR had a density of approximately 0.2Wm.

Example 37 Condensation-Cure VSR Based on a VPCB (15 wt % TFSReinforcement and 70% TMB in 65% VTAS-Crosslinked 90-120 cSt STPDMS),Blended and Crosslinked Using AMA

A partially crosslinked silicone fluid was made by adding 19.993 g VTAS(65% saturation) to 834.3 g 90-120 cSt STPDMS. Prior to this addition,the STPDMS was degassed in vacuum for 3 minutes. The fluid was allowedto cure uncovered at room temperature for 24 hours, at which time itsviscosity had increased to approximately 1000 cSt, approximately 10times its starting value.

To this partially crosslinked STPDMS, 15 wt % TFS was added anddispersed using a 3-roll mill. To 948.8 g of this reinforced mixture,0.949 g of ISAN (0.1 wt %) and 9.533 g of TMB (70% saturation) wereadded. The resulting VPCB was stirred until homogeneous, then spread outto dry at room temperature as a thin layer on a polyethylene plate.

To 5.0 g of this VPCB were added 0.050 g AMA (1 wt %) and the blend waskneaded until homogeneous. It was formed into a disk and placed on apolyethylene sheet to cure for several days. The resulting VSR had aShore Hardness of 53O at t=0, 41O at t=5 sec, and 22O at t=60 sec.

Example 38 Passivation of a VSR with Silicone Sealant (Wacker A07)

The surface of a self-sticky VSR was coated with a thin layer of RTVsilicone sealant (Wacker A07) and that sealant was allowed to cureovernight. The sealant formed a tight bond to the VSR surface andpassivated it completely. A 40 wt % solution of that same sealant inanhydrous toluene worked equally well at passivating the other side ofthe same VSR.

Example 39 Passivation of a VSR with a Titanium Isopropoxide Solution

A 10 wt % solution of TIP in toluene was prepared. The surface of aself-sticky VSR was coated with a thin layer of that solution. The VSRalmost immediately lost its'stickiness and was completely passivated.Its surface felt like that of an ordinary silicone rubber, and itexhibited no self-adhesion.

Example 40 Passivation of a VSR with AMA

The surface of a self-sticky VSR was coated with a thin layer of AMA andallowed to cure overnight. The VSR lost its stickiness and wascompletely passivated.

Example 41 50% HTV Silicone and 50% 90-120 cSt STPDMS-Based100%-Saturated Borosilicone, Softened with Acetic Acid and CrosslinkedUsing DCP

A 90-120 cSt STPDMS-Based 100%-Saturated borosilicone was prepared bydissolving 15.470 g of BA in 172 g of IP and adding the solution to1572.8 g of 90-120 cSt STPDMS. This mixture was heated to 90° C. for 2days to evaporate the solvent, and volatile reaction products and form aborosilicone VSR. The resulting borosilicone VSR was further dried byheating at 180° C. in a convection oven for 4 hours.

6.0 g of this 100% borosilicone was combined with 0.030 g of acetic acid(0.5 wt %) to obtain a softened borosilicone. This softened borosiliconewas then blended with 6.0 g of Wacker R401/60 HTV (high-temperaturevulcanizing) silicone and 0.360 g of 25% DCP (3 wt %) peroxidecrosslinking agent. The completed mixture was cured at 165° C. for 60minutes and became a VSR. The sample was put in a 200° C. oven for 4hours as post-cure.

This VSR exhibited stretched exponential stress relaxation followingsudden compressive or tensile strain. Its elastic modulus was measuredto be 72 kPa and its viscous modulus to be 1.0 MPa. Its Shore Hardnesswas determined to be 40A, 52O at t=0 and 6A, 22O at t=60 sec.

Example 42 50% HTV Silicone and 50% 16-32 cSt STPDMS-Based100%-Saturated Borosilicone, Softened with Acetic Acid and CrosslinkedUsing DCP

A 16-32 cSt STPDMS-Based 100%-Saturated borosilicone was made by adding1.261 g TMB (100% saturation) to 10 g 16-32 cSt STPDMS. The mixture wasallowed to dry for several days until it became a solid film. 0.060 g ofacetic acid (0.5 wt %) was added to the solid borosilicone to obtain asoftened borosilicone. This softened borosilicone was then blended with11.3 g of Wacker R401/60 HTV (high-temperature vulcanizing) silicone and0.670 g of 25% DCP (3 wt %) peroxide crosslinking agent. This completedmixture was cured at 165° C. for 30 minutes, and a VSR was obtained. Thesample was put in a 200° C. oven for 4 hours as post-cure.

This VSR exhibited stretched exponential stress relaxation followingsudden compressive or tensile strain. Its elastic modulus was measuredto be 200 kPa and its viscous modulus to be 4.2 MPa. Its Shore Hardnesswas determined to be 68A, 72O at t=0 and 12A, 31O at t=60 sec.

Example 43 50% HTV Silicone and 50% 90-120 cSt STPDMS-Based100%-Saturated Borosilicone, Softened with Acetic Acid and CrosslinkedUsing VX

The same 90-120 cSt STPDMS-Based 100%-Saturated borosilicone as inExample 41 was prepared. 10.5 g of the 100% borosilicone was combinedwith 0.026 g of acetic acid (0.25 wt %) to obtain a softenedborosilicone. This softened borosilicone was then combined with 10.7 gof Wacker R401/60 HTV (high-temperature vulcanizing) silicone and 0.107g VX (0.5 wt %) peroxide crosslinking agent. This completed mixture wascured at 165° C. for 30 minutes to obtain a VSR.

This VSR exhibited stretched exponential stress relaxation followingsudden compressive or tensile strain. Its elastic modulus was measuredto be 93 kPa and its viscous moduli is to be 1.1 MPa. Its Shore Hardnesswas determined to be 36A, 48O at t=0 and 7A, 18O at t=60 sec.

Example 44 2 wt % Expancels in 75% HTV Silicone and 25% 90-120 cStSTPDMS-Based 100%-Saturated Borosilicone, Softened with Acetic Acid andCrosslinked Using VX

The same 90-120 cSt STPDMS-Based 100%-Saturated borosilicone as inExample 41 was prepared. 1.5 g of the 100% borosilicone was combinedwith 0.0038 g of acetic acid (0.25 wt %) to obtain a softenedborosilicone. This softened borosilicone was then blended with 4.5 g ofWacker R401/60 HTV (high-temperature vulcanizing) silicone, 0.121 gExpancel 930 DU 120 (2 wt %), and 0.032 g VX (0.54 wt %) peroxidecrosslinking agent. This completed mixture was cured at 165° C. for 15minutes to obtain a VSR.

This resulting foamed VSR had a low density, was resilient upon impact,and deformed slowly in response to sustained stress. Its Shore Hardnesswas 33A, 46O at t=0 and 22A, 35O at t=60 sec.

Example 45 50% HTV Silicone and 50% RN Borosilicone and VX

An HTV (high-temperature vulcanizing) silicone and an RN(room-temperature vulcanizing) borosilicone were blended. Both types ofcures were initiated. 20 wt % TFS in 90-120 cSt STPDMS was dispersedusing a 3-roll mill. 65% Saturation of TMB was added to this blend, andthe volatile components were allowed to evaporate. 10 g of this dried65% borosilicone was then combined with 0.330 g of AMA (3.3 wt %), 0.106g PDEOS (40% Saturation), 0.124 g VX (>0.54 wt %), and 10 g Wacker.R401/60 HTV silicone. The mixture cured overnight at 63° C. via aroom-temperature (condensation reaction) cure. The resulting materialwas a viscoelastic solid.

A high-temperature cure was then initiated by heating the mixture to165° C. for 15 minutes. The result was a robust VSR.

This VSR exhibited stretched exponential stress relaxation followingsudden compressive or tensile strain. Its elastic modulus was measuredto be 760 kPa and its viscous modulus to be 4.0 MPa. Its Shore Hardnesswas 60A, 68O at t=0 and 42A, 54O at t=60 sec.

Example 46 45% TEOS and 63% TMB in 30 wt % TFS Reinforced 90-120 cStSTPDMS

30 wt % TFS was dispersed in 90-120 cSt STPDMS using a 3-roll mill. To13.0 g of this blend, 0.200 g AMA (2 wt %), 0.050 g acetic acid (0.5 wt%), 0.112 g TEOS (45% Saturation), and 0.104 g TMB (63% Saturation) wereadded. The mixture was degassed in vacuum, placed in a mold, and allowedto cure and dry at 63° C. in a dehydrator. The resulting material washighly viscoelastic.

This VSR exhibited stretched exponential stress relaxation followingsudden compressive or tensile strain. Its elastic modulus was measuredto be 190 kPa and its viscous modulus to be 2.2 MPa. Its Shore Hardnesswas 53A, 67O at t=0 and 30A, 45O at t=60 sec.

Example 47 Passivation of a VSR with a Titanium Isopropoxide Solution

A VSR sample was prepared using the same procedure as Example 56. ThisVSR had a somewhat sticky surface and exhibited strong self-adhesion.

A 10 wt % solution of TIP in toluene was prepared and a thin coating ofthat solution was painted on the surface of the VSR. The VSR almostimmediately lost its stickiness. Its surface felt like that of anordinary silicone rubber, and it exhibited no self-adhesion.

Example 48 50% VPCB, 25% HTV Silicone, and 25% Borosilicone, Blended andCrosslinked Using 200% PMHS-PDMS Copolymer and Platinum Catalyst

A partially crosslinked silicone fluid was made by adding 5.239 g VTAS(90% Saturation) to 676.7 g 700-800 cSt STPDMS. Prior to this addition,the STPDMS was carefully dried and degassed by stirring it vigorously invacuum for 90 minutes. The fluid bubbled rapidly as moisture and othervolatiles boiled out of it, but after 90 minutes it stopped bubbling.The VTAS was added to the dried STPDMS fluid in a nitrogen-filled glovebox and the mixture was returned to vacuum. It was stirred rapidly undervacuum for 5 minutes, when it again stopped bubbling. The mixture wassealed under an aluminum foil lid and warmed to 60° C. for 18 hours. Itwas then uncovered and allowed to continue curing at room temperaturefor 24 hours. At that time, the fluid's viscosity had increased toapproximately 33,000 cSt, almost 50 times its starting value.

To this partially crosslinked STPDMS, 15 wt % TFS was added anddispersed using a 3-roll mill. To 713.8 g of this reinforced mixture,0.310 g of ISAN (0.05 wt %) and 3.586 g of TMB (150% Saturation) wereadded. The resulting VPCB (VPCB-1) was stirred until homogeneous, thenspread out to dry at room temperature as a thin layer on a polyethyleneplate.

A moderated platinum solution (Platinum-1) was prepared by dispersing 5wt % Pt (3-3.5% Platinum-divinyltetramethyldisiloxane complex, Karstedtcatalyst—Gelest SIP6830.3) and 10 wt % TVTMTS(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxanemoderator—Gelest SID4613.0) in 350 cSt STPDMS.

To 5.5 g of VPCB-1 were combined with 2.75 g of HTV silicone (WackerR401/50), 2.75 g borosilicone (100% BA in 90-120 cSt STPDMS), and 0.010g acetic acid. The resulting 50/25/25 blend was kneaded untilhomogeneous and then 0.200 g PMHS-PDMS copolymer (approximately 200%Saturation) and 0.050 g of Platinum-1 were added. The mixture waskneaded until homogeneous and then pressed into an aluminum mold with aTeflon lid. It was heated to 110° C. for 30 minutes and underwent theaddition cure. It was removed from its mold and kept at 60° C. for 18hours to complete its cure.

This sample exhibits stretched exponential relaxation, a form ofrelaxation first observed by Kohlrausch (Ann. Phys. Leipzig 12, 393(1847)) and expressed in the formula:q(t)=q ₀exp[−(t/τ)^(β)],where t is time, q(t) is the physical characteristic being described bythe relaxation, q₀ is that characteristic at time t=0, τ is acharacteristic time constant, and 6 is the stretching exponent and is0≦β≦1. For β=1, this relaxation process is ordinary exponentialrelaxation. The as-cured sample had a characteristic time constant of481 seconds and a stretching exponent of 0.29.

That extremely slow relaxation rate suggests that the boron-bridgecrosslinks in this as-cured sample were more permanent than temporary. Alikely explanation for that result is that the PMHS-PDMS copolymer,present in substantial excess in the pre-cure mixture, reacted withvirtually all of the hydroxyl, carboxyl, and silanol groups in themixture during the addition cure and left the as-cured sample nearlydevoid of reactive groups that could open the boron-bridge crosslinks.With almost no boron-bridge-opening-chemicals present, the VSR appearedapproximately elastic on timescales shorter than 1 minute. This as-curedVSR had a Shore Hardness of 42O at t=0, 42O at t=5 sec, and 41O at t=60sec.

Exposing this sample to 60% relative humidity air at 20° C. for 30 daysreduced its characteristic time constant to 6.6 seconds and increasedits stretching exponent of 0.62. This faster relaxation rate suggeststhat the boron-bridge crosslinks in this atmosphere-equilibrated sampleare truly temporary. A likely explanation for that result is thatatmospheric moisture diffused into the sample and acted as aboron-bridge-opening-chemical, thereby allowing the sample to exhibitviscoelastic behavior on a timescale shorter than 1 minute. Thisatmosphere-equilibrated VSR had a Shore Hardness of 42O at t=0, 32O att=5 sec, and 19O at t=60 sec.

Example 49 Arizona Century 1105 Softened 60% MTEOS and 50% TMB in 15 wt% TFS-Reinforced 90-120 cSt STPDMS

15 wt % TFS was dispersed in 90-120 cSt STPDMS using a 3-roll mill. To40.0 g of this blend, 0.800 g Arizona Century 1105 (2 wt %), 0.289 g TMB(50% Saturation), 0.700 g AMA (2 wt %), and 0.594 g MTEOS (60%Saturation) were added. The mixture was degassed in vacuum, placed in asheet mold measuring 3″×3″×0.1875″, and allowed to cure for 24 hours at60° C. in a dehydrator. This VSR has a somewhat greasy surface.

Example 50 Peroxide-Cure VSR Based on 50% HTV Silicone and 50% (90-120cSt STPDMS-Based 200%-Saturated Titanosilicone), Blended and CrosslinkedUsing VX

90-120 cSt STPDMS-based 100%-Saturated titanosilicone was prepared byadding 3.384 g TIP (200% saturation) to 50.0 g 90-120 cSt STPDMS. Themixture was heated to 175° C. for 4 hours in a convection oven toevaporate the volatile reaction products. The mixture was further driedas a thin sheet at 63° C. in a dehydrator overnight.

16.0 g of the titanosilicone was combined with 16.0 g of Wacker R401/50HTV silicone and kneaded together until the mixture was homogeneous.0.080 g of VX crosslinker was added, and the mixture was kneaded againuntil homogeneous. The sticky, viscous blend was squeezed into a Teflonsheet mold, 3″×3″×0.1875″ deep, and the mold was capped with a Teflonsheet and placed it in an aluminum press, which was bolted closed withthe help of a 20 ton hydraulic press. The press and mold assembly wereheated to 165° C. for 30 minutes. After cooling the mold to roomtemperature, the finished VSR sample was removed.

This VSR had a Shore Hardness of 18A, 43O at t=0, 4A, 24O at t=5 sec,and 0A, 10O at t=60 sec. It was stickier than borosilicone-based VSRs.

Example 51 Peroxide-Cure VSR Based on 50% HTV Silicone and 50%(ISAN-Softened 90-120 cSt STPDMS-Based Borotitanosilicone), Blended andCrosslinked Using VX

ISAN softened 90-120 cSt STPDMS-based 100%-Saturated borotitanosiliconewas made by adding 0.550 g TMB (67% saturation), 0.558 g TIP (33%saturation), and 0.125 g ISAN (0.25 wt %) to 50.0 g 90-120 cSt STPDMS.The mixture was heated to 175° C. for 4 hours in a convection oven toevaporate the volatile reaction products and further dried as a thinsheet at 63° C. in a dehydrator overnight.

To 16.0 g of the borotitanosilicone, 0.050 g TMB (25% saturation) wasadded, and the mixture was allowed to dry in the dehydrator at 63° C.for several hours. The mixture was then combined with 16.0 g of WackerR401/50 HTV silicone and kneaded together until the mixture washomogeneous. 0.080 g of VX crosslinker was added and the mixture waskneaded again until homogeneous. The sticky, viscous blend was squeezedinto a Teflon sheet mold, 3″×3″×0.1875″ deep, and the mold was cappedwith a Teflon sheet and placed it in an aluminum press, which was boltedclosed with the help of a 20 ton hydraulic press. The press and moldassembly was heated to 165° C. for 30 minutes. After cooling the mold toroom temperature, the finished VSR sample was removed.

This VSR had a Shore Hardness of 14A, 40O at t=0, 3A, 16O at t=5 sec,and 0A, 6O at t=60 sec. It was much stickier than borosilicone-basedVSRs.

Example 52 25%, 30%, 35%, 40%, 50%, 60% VTAS in 90-120 cSt STPDMS and30%, 40%, 50%, 60% MTEOS in 90-120 cSt STPDMS, Blended and Cured withAMA

Ten 20 g samples of 90-120 cSt STPDMS were prepared. To these tensamples were added, respective: 0.184 g VTAS (25% saturation), 0.221 gVTAS (30% saturation), 0.258 g VTAS (35% saturation), 0.295 g VTAS (40%saturation), 0.369 g VTAS (50% saturation), 0.442 g VTAS (60%saturation), 0.170 g MTEOS (30% saturation), 0.226 g MTEOS (40%saturation), 0.283 g MTEOS (50% saturation), 0.340 g MTEOS (60%saturation).

To each of the ten samples, 0.050 g AMA (0.25 wt %) were added andstirred in carefully. The ten samples were warmed to 60° C. and allowedto cure for approximately 24 hours. All ten samples cured to form solidsilicone elastomers, although the 30% MTEOS and 40% MTEOS samples werequite soft.

The gelation thresholds for VTAS or MTEOS in STPDMS, predictedtheoretically by Flory (Paul J. Flory, J. Phys. Chem. 46, 132 (1942)),Stockmayer (Walter H. Stockmayer, J. Chem. Phys. 11, 45 (1943)), andothers occurs at 50% saturation. That 25% VTAS and 30% MTEOS were ableto cure STPDMS and form solid silicone elastomers suggests thatconsiderable homocondensation of the STPDMS chains occurred, perhapsfacilitated by the AMA catalyst. By eliminating many of the silanolgroups, this homocondensation increased the effective saturation levelsof VTAS and MTEOS and caused these samples to exceed the gelationthreshold and become solid silicone elastomers.

Example 53 60% MTEOS and 30% TMB in 15 wt % TFS-Reinforced 90-120 cStSTPDMS

15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using athree-roll mill. To 40.0 g of this blend were added one at a time:<0.020 g pigment, 0.198 TMB (30% Saturation), 0.040 g acetic acid (0.1wt %), 0.679 g MTEOS (60% saturation), and 0.400 g AMA (1 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum, poured into a sheet mold that measured3″×3″×0.1875″ and allowed to cure and dry for 24 hours at 60° C. in adehydrator. It was then removed from its mold. This VSR was kept at 60°C. for an additional month to ensure that it was completely cured anddried, and that all the acetic acid had evaporated. It has ShoreHardness 57O at t=0 and 43O at t=600 sec.

Example 54 55% MTEOS and 35% TMB in 15 wt % TFS-Reinforced 90-120 cStSTPDMS

15 wt % TF5 (Cabot) was dispersed in 90-120 cSt STPDMS using athree-roll mill. To 40.0 g of this blend were added one at a time:<0.020 g pigment, 0.231 TMB (35% Saturation), 0.040 g acetic acid (0.1wt %), 0.623 MTEOS (55% saturation), and 0.400 g AMA (1 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum, pouring into a sheet mold that measured3″×3″×0.1875″ and allowed to cure and dry for 24 hours at 60° C. in adehydrator. It was then removed from its mold. This VSR was kept at 60°C. for an additional month to ensure that it was completely cured anddried, and that all the acetic acid had evaporated. It has ShoreHardness 55O at t=0 and 37O at t=600 sec.

Example 55 50% MTEOS and 40% TMB in 15 wt % TFS-Reinforced 90-120 cStSTPDMS

15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using athree-roll mill. To 40.0 g of this blend were added one at a time:<0.020 g pigment, 0.264 TMB (40% Saturation), 0.040 g acetic acid (0.1wt %), 0.566 MTEOS (55% saturation), and 0.400 g AMA (1 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum, poured into a sheet mold that measured3″×3″×0.1875″ and allowed to cure and dry for 24 hours at 60° C. in adehydrator. It was then removed from its mold. This VSR was kept at 60°C. for an additional month to ensure that it was completely cured anddried, and that all the acetic acid had evaporated. It has ShoreHardness 56O at t=0 and 33O at t=600 sec.

Example 56 45% MTEOS and 45% TMB in 15 wt % TFS-Reinforced 90-120 cStSTPDMS

15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using athree-roll mill. To 40.0 g of this blend were added one at a time:<0.020 g pigment, 0.297 TMB (45% Saturation), 0.040 g acetic acid (0.1wt %), 0.509 MTEOS (45% saturation), and 0.400 g AMA (1 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum, poured into a sheet mold that measured3″×3″×0.1875″ and allowed to cure and dry for 24 hours at 60° C. in adehydrator. It was then removed from its mold. This VSR was kept at 60°C. for an additional month to ensure that it was completely cured anddried, and that all the acetic acid had evaporated. It has ShoreHardness 54O at t=0 and 28O at t=600 sec.

Example 57 35% MTEOS and 35% TMB in 15 wt % TFS-Reinforced 90-120 cStSTPDMS

15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using athree-roll mill. To 40.0 g of this blend were added one at a time:<0.020 g pigment, 0.231 TMB (35% Saturation), 0.040 g acetic acid (0.1wt %), 0.396 MTEOS (35% saturation), and 0.400 g AMA (1 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum, poured into a sheet mold that measured3″×3″×0.1875″ and allowed to cure and dry for 24 hours at 60° C. in adehydrator. It was then removed from its mold. This VSR was kept at 60°C. for an additional month to ensure that it was completely cured anddried, and that all the acetic acid had evaporated. It has ShoreHardness 50O at t=0 and 25O at t=600 sec.

Example 58 60% MTEOS and 30% TMB in 15 wt % TFS-Reinforced 700-800 cStSTPDMS

20 wt % TFS (Gelest) was dispersed in 700-800 cSt STPDMS using athree-roll mill. To 40.0 g of this blend were added one at a time:<0.020 g pigment, 0.046 TMB (30% Saturation), 0.040 g acetic acid (0.1wt %), 0.159 MTEOS (60% saturation), and 0.400 g AMA (1 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum, poured into a sheet mold that measured3″×3″×0.1875″ and allowed to cure and dry for 24 hours at 60° C. in adehydrator. It was then removed from its mold. This VSR was kept at 60°C. for an additional month to ensure that it was completely cured anddried, and that all the acetic acid had evaporated. It has ShoreHardness 33O at t=0 and 17O at t=600 sec.

Example 59 60% MTEOS and 35% TMB in 15 wt % TFS-Reinforced 90-120 cStSTPDMS

15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using athree-roll mill. To 52.0 g of this blend were added one at a time:<0.020 g pigment, 0.261 TMB (35% Saturation), 0.052 g acetic acid (0.1wt %), 0.768 g MTEOS (60% saturation), and 0.400 g AMA (0.8 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum and 40 g were poured into a sheet mold thatmeasured 3″×3″×0.1875″. The sample was allowed to cure and dry for 24hours at 60° C. in a dehydrator. It was then removed from its mold. ThisVSR was kept at 60° C. for an additional month to ensure that it wascompletely cured and dried, and that all the acetic acid had evaporated.It has Shore Hardness 58O at t=0, 56O at t=5 sec, 51O at t=60 sec, 42Oat t=300 sec, and 36O at t=600 sec.

Example 60 0.1 wt % ISA, 60% MTEOS, and 35% TMB in 15 wt %IFS-Reinforced 90-120 cSt STPDMS

15 wt % TFS (Cabot) was dispersed in 90-120 cSt STPDMS using athree-roll mill. To 52.0 g of this blend were added one at a time:<0.020 g pigment, 0.261 TMB (35% Saturation), 0.052 g acetic acid (0.1wt %), 0.768 g MTEOS (60% saturation), and 0.400 g AMA (0.8 wt %). Theblend's viscosity increased significantly upon the addition of TMB, butdecreased significantly upon addition of the acetic acid. The mixturewas degassed in vacuum and 40 g were poured into a sheet mold thatmeasured 3″×3″×0.1875″. The sample was allowed to cure and dry for 24hours at 60° C. in a dehydrator. It was then removed from its mold. ThisVSR was kept at 60° C. for an additional month to ensure that it wascompletely cured and dried, and that all the acetic acid had evaporated.It has Shore Hardness 580 at t=0, 49O at t=5 sec, 33O at t=60 sec, 29Oat t=300 sec, and 26O at t=600 sec.

Example 61 Passivation of a VSR with a Titanium Isopropoxide Solution

A 10 g VSR disk, compositionally equivalent to Example 29, was paintedwith a thin layer of Struksilon 8018. The painted disk became relativelynon-sticky and would not stick to itself or to other VSRs. In contrast,an unpainted disk of the same VSR was somewhat sticky and would stick toitself temporarily.

Example 62 VSR Made from Sulfuric-Acid-Treated Partially CrosslinkedSTPDMS, Using the Peroxide Cure

A partially crosslinked STPDMS fluid was prepared by combining 50.0 g ofdried 90-120 cSt STPDMS (Gelest DMS-S21) and 0.737 g VTAS. The STPDMShad been dried by heating it to 100° C. and bubbling dry nitrogenthrough it for 24 hours. After curing at 60° C. for more than 72 hours,this partially crosslinked STPDMS fluid was allowed to cool to roomtemperature. It remained a low-viscosity liquid.

To 7.0 g of that fluid was added approximately 1 mg of sulfuric acid.The mixture was stirred vigorously under vacuum and its viscosity beganto increase. When its viscosity had reached approximately 15,000 cSt,0.116 g of TMB (100% saturation) were added and the fluid became aborosilicone. After kneading the borosilicone in a slip roll, it wasallowed to dry overnight.

To the 7.0 g of borosilicone were added 0.007 g iso-stearic acid (0.1 wt%), 0.007 g acetic acid (0.1 wt %), and 0.070 g VX (1.0 wt %). Afterkneading to homogeneity, the blend was pressed into a Teflon disk moldand vulcanized at 165° C. for 30 minutes. The resulting disk was a VSR.

Example 63 VPCB with 0.1M Vinyl Groups Per Kilogram Made fromSulfuric-Acid-Treated Partially Crosslinked STPDMS

A partially crosslinked STPDMS fluid was prepared by combining 500.0 gof dried 90-120 cSt STPDMS (Gelest DMS-S21) and 11.613 g VTAS. TheSTPDMS had been dried by degassing it in vacuum for 20 minutes. Thefluid was allowed to cure in a sealed container for 7 days at 60° C. andthen cooled to room temperature. Its finished viscosity wasapproximately 420 cSt.

A 5% dispersion of 0.250 g sulfuric acid in 5.0 g of 350 cSt PDMSsilicone fluid was prepared. Rapid shaking resulted in microscopicdroplets of sulfuric acid suspended in the silicone fluid.

To 50.0 g of the partially crosslinked STPDMS was added 0.044 g of the5% sulfuric acid dispersion. The mixture was stirred carefully and itsviscosity monitored at approximately 30 minute intervals. After 228minutes, its viscosity had increased to approximately 8100 cSt. To thisthickened fluid was added 0.020 g of precipitated calcium carbonatepowder (Solvay Winnofil SPM). The mixture was stirred carefully tofacilitate neutralization of the sulfuric acid.

To the fluid were added 1.5 g of TMB. When stirred, this mixtureimmediately thickened into a borosilicone putty. The density of vinylgroups in this VPCB is approximately 0.1 M/kg.

Example 64 VPCB with 0.075M Vinyl Groups Per Kilogram Made fromSulfuric-Acid-Treated Partially Crosslinked STPDMS

A partially crosslinked STPDMS fluid was prepared by combining 500.0 gof dried 90-120 cSt STPDMS (Gelest DMS-S21) and 8.710 g VTAS. The STPDMShad been dried by degassing it in vacuum for 20 minutes. The fluid wasallowed to cure in a sealed container for 7 days at 60° C. and thencooled to room temperature. Its finished viscosity was approximately 160cSt.

To 50.0 g of the partially crosslinked STPDMS was added 0.043 g of the5% sulfuric acid dispersion from Example 63. The mixture was stirredcarefully and its viscosity monitored at approximately 30 minuteintervals. After 191 minutes, its viscosity had increased toapproximately 840 cSt and was no longer changing. The was then vacuumdegassed and its viscosity began to increase rapidly. After 2 hours invacuum, its viscosity had reached 12,800 cSt. To this thickened fluidwas added 0.020 g of precipitated calcium carbonate powder (SolvayWinnofil SPM). The mixture was stirred carefully to facilitateneutralization of the sulfuric acid.

To the fluid was added 0.50 g of TMB. When stirred, this mixtureimmediately thickened into a borosilicone putty. The density of vinylgroups in this VPCB is approximately 0.075 M/kg.

Example 65 VPCB with 0.05M Vinyl Groups Per Kilogram Made fromSulfuric-Acid-Treated Partially Crosslinked STPDMS

A partially crosslinked STPDMS fluid was prepared by combining 500.0 gof dried 90-120 cSt STPDMS (Gelest DMS-S21) and 5.807 g VTAS. The STPDMShad been dried by degassing it in vacuum for 20 minutes. The fluid wasallowed to cure in a sealed container for 7 days at 60° C. and thencooled to room temperature. Its finished viscosity was approximately 100cSt.

To 50.0 g of the partially crosslinked STPDMS was added 0.043 g of the5% sulfuric acid dispersion from Example 63. The mixture was stirredcarefully and its viscosity monitored at approximately 30 minuteintervals. After 187 minutes, its viscosity had increased toapproximately 360 cSt and was no longer changing. The fluid was thenvacuum degassed and its viscosity began to increase rapidly. After 3hours in vacuum, its viscosity had reached 11,100 cSt. To this thickenedfluid was added 0.020 g of precipitated calcium carbonate powder (SolvayWinnofil SPM). The mixture was stirred carefully to facilitateneutralization of the sulfuric acid.

To the fluid was added 0.40 g of TMB. When stirred, this mixtureimmediately thickened into a borosilicone putty. The density of vinylgroups in this VPCB is approximately 0.05 M/kg.

Example 66 VPCB with 0.033M Vinyl Groups Per Kilogram Made fromSulfuric-Acid-Treated Partially Crosslinked STPDMS

A partially crosslinked STPDMS fluid was prepared by combining 100.0 gof dried 90-120 cSt STPDMS (Gelest DMS-S21), 400.0 g of dried 700-800cSt STPDMS (Gelest DMS-S27), and 3.832 g VTAS. The STPDMS had been driedby degassing it in vacuum for 20 minutes. The fluid was allowed to curein a sealed container for 7 days at 60° C. and then cooled to roomtemperature. Its finished viscosity was approximately 11,400 cSt.

To 50.0 g of the partially crosslinked STPDMS was added 0.041 g of the5% sulfuric acid dispersion from Example 63. The mixture was stirredcarefully and its viscosity monitored at approximately 30 minuteintervals. After 148 minutes, its viscosity had increased toapproximately 36,700 cSt. To this thickened fluid was added 0.018 g ofprecipitated calcium carbonate powder (Solvay Winnofil SPM). The mixturewas stirred carefully to facilitate neutralization of the sulfuric acid.

To the fluid was added 0.40 g of TMB. When stirred, this mixtureimmediately thickened into a borosilicone putty. The density of vinylgroups in this VPCB is approximately 0.033 M/kg.

Example 67 VPCB with 0.025M Vinyl Groups Per Kilogram Made fromSulfuric-Acid-Treated Partially Crosslinked STPDMS

A partially crosslinked STPDMS fluid was prepared by combining 500.0 gof dried 700-800 cSt STPDMS (Gelest DMS-S27) and 2.903 g VTAS. TheSTPDMS had been dried by degassing it in vacuum for 20 minutes. Thefluid was allowed to cure in a sealed container for 7 days at 60° C. andthen cooled to room temperature. Its finished viscosity wasapproximately 17,200 cSt.

To 50.0 g of the partially crosslinked STPDMS was added 0.041 g of the5% sulfuric acid dispersion from Example 63. The mixture was stirredcarefully and its viscosity monitored at approximately 30 minuteintervals. After 151 minutes, its viscosity had increased toapproximately 49,200 cSt. To this thickened fluid was added 0.015 g ofprecipitated calcium carbonate powder (Solvay Winnofil SPM). The mixturewas stirred carefully to facilitate neutralization of the sulfuric acid.

To the fluid was added 0.35 g of TMB. When stirred, this mixtureimmediately thickened into a borosilicone putty. The density of vinylgroups in this VPCB is approximately 0.025 M/kg.

Example 68 VPCB Made from Partially Crosslinked 90-120 cSt STPDMS Curedat 200° C.

100.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) was heated to 140° C. and,while stirring rapidly with a magnetic stirrer, 2.58 g VTAS was added.The mixture was further heated to about 200° C. and the stirringcontinued. After 50 minutes, the viscosity of the mixture was still lowso an additional 0.368 g of VTAS was added. The fluid began to gelwithin seconds. Before the fluid could solidify, it was cooled quicklyto room temperature and approximately 0.165 g TMB were added to convertit to a VPCB. It was left to dry in the open air overnight.

Example 69 VPCB Made from Partially Crosslinked 90-120 cSt STPDMS Curedat 190° C.

100.0 g of 90-120 cSt STPDMS (Gelest DMS-S21, Lot BE-12804) was heatedto 165° C. and, while stirring rapidly with a magnetic stirrer, 2.77 gVTAS was added. The mixture was further heated to about 190° C. and thestirring continued. After 60 minutes, the viscosity of the mixture beganto increase noticeably. After 80 minutes, the mixture had partiallygelled. Before the fluid could solidify, it was cooled quickly to roomtemperature and approximately 0.165 g TMB were added to convert it to aVPCB. It was left to dry in the open air overnight.

Example 70 VPCB Made from Partially Crosslinked 90-120 cSt STPDMS Curedat 190° C.

100.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) was heated to 150° C. and,while stirring rapidly with a magnetic stirrer, 2.40 g VTAS was added.The mixture was further heated to about 190° C. and the stirringcontinued. After 60 minutes, the viscosity of the mixture began toincrease noticeably. After 80 minutes, the mixture's viscosity hadincreased to the point where the magnetic stirrer could no longer turnproperly. The fluid was cooled to room temperature and approximately0.165 g TMB were added to convert it to a VPCB. It was left to dry inthe open air overnight.

Example 71 VPCB Made from Partially Crosslinked 700-800 cSt STPDMS Curedat 182° C.

300.0 g of 700-800 cSt STPDMS (Gelest DMS-S27) was heated to 150° C.and, while stirring rapidly with a magnetic stirrer, 2.44 g VTAS wasadded. The mixture was further heated to about 182° C. and the stirringcontinued. After 90 minutes, the viscosity of the mixture began toincrease noticeably. The fluid was cooled to about 100° C. and 2.3 g ofTMB were added to convert it to a VPCB. It was left to dry in the openair overnight.

Example 72 VPCB Made from Partially Crosslinked 90-120 cSt STPDMS Curedat 180° C.

400.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) was heated to 100° C. and8.848 g VTAS was added while stirring at 500 rpm with a high-shearimmersion blade. The temperature was increased gradually to about 180°C. After 170 minutes, drips of fluid from a glass rod produced stringytails. The vulcanizable partially crosslinked silicone fluid was allowedto cool to room temperature and its viscosity was measured at about 2700cSt. When TMB was added to a small portion of this fluid, it immediatelyformed a VPCB.

Example 73 VPCB Made from Partially Crosslinked 90-120 cSt STPDMS Curedat 180° C.

400.0 g of 90-120 cSt STPDMS (Gelest DMS-S21) that had been stored in anopen container for several months was heated to 100° C. and 9.585 g VTASwas added while stirring at 250 rpm with a high-shear immersion blade.The temperature was increased gradually to about 180° C. After 220minutes, drips of fluid from a glass rod produced stringy tails. Thevulcanizable partially crosslinked silicone fluid was allowed to cool toroom temperature and its viscosity was measured at about 7000 cSt. WhenTMB was added to a small portion of this fluid, it immediately formed aVPCB.

Example 74 Peroxide-Cure VSR Based on 67% VPCB (4.5 wt % VTAS and 1.7 wt% TMB in 70 cSt STPDMS) and 33% High-Consistency Silicone Rubber (HCR)(Wacker R420/50), Blended and Softened with 0.5 wt % Oleic Acid, andCrosslinked Using 0.57 wt % VX Peroxide

3069.0 g of 70 cSt STPDMS (Masil SFR 70, Emerald Performance Materials)was dried in vacuum for 5 minutes. To this fluid was slowly added 138.1g VTAS while stirring rapidly. The beaker containing this mixture washeated to approximately 120° C. in a convection oven for 350 minutes andthe partially crosslinked silicone fluid was then allowed to cool. Thedynamic viscosity of this PCS at room temperature was 300 mPa·s.

To 50.0 g of the PCS were added 0.375 g oleic acid (0.50 wt %) and then0.850 g of TMB (1.7 wt %). The viscous mixture was vacuum dried forabout 5 minutes. 25.0 g of HCR silicone (Wacker Elastosil R420/50) wereadded and the blend was kneaded to homogeneity in a slip roll. It wasspread as thin sheets on Teflon and allowed to equilibrate and dry forseveral hours at 70° C.

To 10.5 g of the blend were added 0.060 g VX (0.57 wt %) and thevulcanizable material was kneaded to homogeneity in the slip roll. Itwas placed in a Teflon mold and cured at 160° C. for 15 minutes. Theresulting viscoelastic silicone rubber had a Shore Hardness of 54O att=0, 32O at t=5 sec, and 19O at t=60 sec.

Example 75 Peroxide-Cure VSR Based on 67% VPCB (3.0 wt % VTAS and 0.95wt % TMB in 100 cSt STPDMS) and 33% HCR (Wacker R420/50), Blended andSoftened with 0.5 wt % Oleic Acid, and Crosslinked Using 0.57 wt % VXPeroxide

3100.0 g of 100 cSt STPDMS (Masil SFR 100, Emerald PerformanceMaterials) was dried in vacuum for 5 minutes. To this fluid was slowlyadded 93.0 g VTAS while stirring rapidly. The beaker containing thismixture was heated to approximately 120° C. in a convection oven for 350minutes and the partially crosslinked silicone fluid was then allowed tocool. The dynamic viscosity of this PCS at room temperature was 510mPa·s.

To 50.0 g of the PCS were added 0.375 g oleic acid (0.50 wt %) and then0.475 g of TMB (0.95 wt %). The viscous mixture was vacuum dried forabout 5 minutes. 25.0 g of HCR silicone (Wacker Elastosil R420/50) wereadded and the blend was kneaded to homogeneity in a slip roll. It wasspread as thin sheets on Teflon and allowed to equilibrate and dry forseveral hours at 70° C.

To 10.5 g of the blend were added 0.060 g VX (0.57 wt %) and thevulcanizable material was kneaded to homogeneity in the slip roll. Itwas placed in a Teflon mold and cured at 160° C. for 15 minutes. Theresulting viscoelastic silicone rubber had a Shore Hardness of 48O att=0, 21O at t=5 sec, and 16O at t=60 sec.

Example 76 Peroxide-Cure VSR Based on 67% VPCB (0.7 wt % VTAS and 0.40wt % TMB in 750 cSt STPDMS) and 33% HCR (Wacker R420/50), Blended andSoftened with 0.4 wt % Oleic Acid, and Crosslinked Using 0.38 wt % VXPeroxide

1172.80 g of 750 cSt STPDMS (Masil SFR 750, Emerald PerformanceMaterials) was dried in vacuum for 5 minutes. To this fluid was slowlyadded 8.210 g VTAS while stirring rapidly. The beaker containing thismixture was heated to approximately 135° C. in a convection oven for 300minutes and the partially crosslinked silicone fluid was then allowed tocool. The dynamic viscosity of this PCS at room temperature was 7000mPa·s.

To 50.0 g of the PCS were added 0.300 g oleic acid (0.40 wt %) and then0.200 g of TMB (0.40 wt %). The viscous mixture was vacuum dried forabout 5 minutes. 25.0 g of HCR silicone (Wacker Elastosil R420/50) wereadded and the blend was kneaded to homogeneity in a slip roll. It wasspread as thin sheets on Teflon and allowed to equilibrate and dry forseveral hours at 70° C.

To 10.5 g of the blend were added 0.040 g VX (0.38 wt %) and thevulcanizable material was kneaded to homogeneity in the slip roll. Itwas placed in a Teflon mold and cured at 160° C. for 15 minutes. Theresulting viscoelastic silicone rubber had a Shore Hardness of 28O att=0, 7O at t=5 sec, and 2O at t=60 sec.

Example 77 Peroxide-Cure VSR Based on 67% VPCB (0.4 wt % VTAS and 0.35wt % TMB in 2000 cSt STPDMS) and 33% HCR (Wacker R420/50), Blended andSoftened with 0.2 wt % Oleic Acid, and Crosslinked Using 0.38 wt % VXPeroxide

1012.8 g of 2000 cSt STPDMS (Masil SFR 2000, Emerald PerformanceMaterials) was dried in vacuum for 5 minutes. To this fluid was slowlyadded 4.051 g VTAS while stirring rapidly. The beaker containing thismixture was heated to approximately 135° C. in a convection oven for 300minutes and the partially crosslinked silicone fluid was then allowed tocool. The dynamic viscosity of this PCS at room temperature was 14,500mPa·s.

To 50.0 g of the PCS were added 0.150 g oleic acid (0.2 wt %) and then0.175 g of TMB (0.40 wt %). The viscous mixture was vacuum dried forabout 5 minutes. 25.0 g of HCR silicone (Wacker Elastosil R420/50) wereadded and the blend was kneaded to homogeneity in a slip roll. It wasspread as thin sheets on Teflon and allowed to equilibrate and dry forseveral hours at 70° C.

To 10.5 g of the blend were added 0.040 g VX (0.38 wt %) and thevulcanizable material was kneaded to homogeneity in the slip roll. Itwas placed in a Teflon mold and cured at 160° C. for 15 minutes. Theresulting viscoelastic silicone rubber had a Shore Hardness of 25O att=0, 11O at t=5 sec, and 5O at t=60 sec.

The claimed invention is:
 1. A viscoelastic silicone rubber compositioncomprising: (a) at least one polyorganosiloxane; (b) at least onepermanent crosslinking agent present in an amount to provide sufficientpermanent crosslinks to give the composition an equilibrium shape whencured; (c) at least one temporary crosslinking agent present in anamount to provide sufficient temporary crosslinks to give thecomposition a stiffness when cured that is greater on short timescalesthan it is on long timescales; and (d) at least one softening agentpresent in an amount sufficient to make the average lifetime of thetemporary crosslink of shorter duration than the average lifetime of thetemporary crosslink in the absence of the softening agent.
 2. Aviscoelastic silicone rubber composition of claim 1 comprising: (a) atleast one polyorganosiloxane comprising at least oneethylenically-unsaturated group.
 3. A viscoelastic silicone rubbercomposition of claim 1 comprising: (a) at least one branchedpolyorganosiloxane.
 4. The viscoelastic silicone rubber composition ofclaim 3, further comprising at least one linear polyorganosiloxane.
 5. Aviscoelastic silicone rubber composition of claim 1, wherein: (a) thepolyorganosiloxane comprises a silanol-terminated polyorganosiloxanepolymers of formula (I)

having a molecular weight ranging from 400 to 50,000 Dalton and aviscosity ranging from 10 to 10,000 cSt and preferably from about 15 to2,000 cSt and wherein “m” is 1 or greater and represents the number ofthe repeating units in parentheses to give the molecular weight of theparticular polymer; (b) the permanent crosslinking agent is selectedfrom a vinyltriacetoxysilane, vinyltrimethoxysilane,vinyltrichlorosilane, and vinyltriethoxysilane; and (c) the temporarycrosslinking agent is selected from a boron-containing compound, atitanium-containing compound, an aluminum-containing compound, or amixture thereof.
 6. The viscoelastic silicone rubber composition ofclaim 1, wherein the polyorganosiloxane is silanol-terminated.
 7. Theviscoelastic silicone rubber composition of claim 1, wherein thepolyorganosiloxane is partially crosslinked and has at least threeterminal silanols.
 8. The viscoelastic silicone rubber composition ofclaim 1, wherein the polyorganosiloxane is branched.
 9. The viscoelasticsilicone rubber composition of claim 1, wherein the permanentcrosslinking agent is a siloxane bond-forming crosslinking agent, acarbon-carbon bond-forming crosslinking agent, or a mixture thereof. 10.The viscoelastic silicone rubber composition of claim 1, wherein thepermanent crosslinks are formed using condensation-cure crosslinking,addition-cure crosslinking, peroxide cure crosslinking, or a mixturethereof.
 11. The viscoelastic silicone rubber composition of claim 1,wherein the permanent crosslinking agent is present in amount rangingfrom about 0.02 wt % to 10.0 wt %.
 12. A viscoelastic silicone rubbercomposition of claim 1, wherein the temporary crosslinking agent isselected from a boron-containing compound.
 13. A viscoelastic siliconerubber composition of claim 12, wherein the boron-containing compound isselected from boric acid, trimethyl borate, triethyl borate, andtri-isopropyl borate.
 14. A viscoelastic silicone rubber composition ofclaim 1, wherein the temporary crosslinking agent is present in amountranging from about 0.01 wt % to 20.0 wt %.
 15. A viscoelastic siliconerubber composition of claim 1, wherein the softening agent is present inan amount sufficient to make the average lifetime of the temporarycrosslink of shorter duration than the average lifetime of the temporarycrosslink in the absence of the softening agent.
 16. A viscoelasticsilicone rubber composition of claim 1, wherein the softening agent ispresent in an amount ranging from about 0.01 wt % to 5.0 wt %.
 17. Aviscoelastic silicone rubber composition of claim 1, further comprisingat least one filler.
 18. A viscoelastic silicone rubber composition ofclaim 1, further comprising at least one additive, or at least onecatalyst, or at least one blowing agent, or at least one passivatingagent.
 19. A shaped article comprising a cured viscoelastic siliconerubber composition of claim
 1. 20. A viscoelastic silicone rubbercomposition of claim 1, wherein the softening agent is selected from thegroup consisting of water, an alcohol, a polyol, an acid, and a base.21. A viscoelastic silicone rubber composition of claim 1, wherein thesoftening agent is selected from the group consisting of isostearylalcohol, isostearic acid, oleic acid, and acetic acid.